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SILICA BODIES IN MONOCOTYLEDONS 377
Issued 00 March 2004
© 2004 The New York Botanical Garden
Copies of this issue [69(4)] may be purchased from the NYBG Press,
The New York Botanical Garden, Bronx, NY 10458-5128, U.S.A.;
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377
The Botanical Review 69(4): 377–440
Systematics and Biology of Silica Bodies in Monocotyledons
CHRISTINA J. PRYCHID, PAULA J. RUDALL, AND MARY GREGORY
Jodrell Laboratory
Royal Botanic Gardens
Kew, Richmond, Surrey TW9 3AB, England
I. Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 377
II. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 378
III. Historical Review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 378
IV. Composition of Silica in Plants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 380
V. Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 380
VI. Uptake and Deposition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 382
VII. Morphology and Location . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 384
VIII. Ecology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 384
IX. Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 385
X. Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 386
A. Soils and Archaeology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 386
B. Agricultural Crops and Their Evolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 387
C. Medical Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 387
D. Animal Diets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 387
E. Other Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 388
XI. Systematic Distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 388
A. Orchidaceae . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 390
B. Commelinids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 398
1. Arecaceae . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 398
2. ZHC Clade (Zingiberales, Commelinales and Hanguana) . . . . . . . . . . . . . . . 401
3. Poales . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 406
4. Dasypogonaceae. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 425
XII. Literature Cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 425
I. Abstract
Many plants take up soluble monosilicic acid from the soil. Some of these plants subse-
quently deposit it as cell inclusions of characteristic structure. This article describes the distri-
bution and diversity of opaline silica bodies in monocotyledons in a phylogenetic framework,
together with a review of techniques used for their examination, and the ecology, function and
economic applications of these cell inclusions. There are several different morphological forms
of silica in monocot tissues, and the number of silica bodies per cell may also vary. The most
common type is the “druse-like” spherical body, of which there is normally a single body per
cell, more in some cases. Other forms include the conical type and an amorphous, fragmentary
type (silica sand). Silica bodies are most commonly found either in the epidermis (e.g., in
378 THE BOTANICAL REVIEW
grasses, commelinas and sedges) or in the sheath cells of vascular bundles (e.g., in palms,
bananas and orchids). Silica-bearing cells are most commonly associated either with subepi-
dermal sclerenchyma or bundle-sheath sclerenchyma. Silica bodies are found only in orchids
and commelinids, not in other lilioid or basal monocots. In orchids, silica bodies are entirely
absent from subfamilies Vanilloideae and Orchidoideae and most Epidendroideae but present
in some Cypripedioideae and in the putatively basal orchid subfamily Apostasioideae. Among
commelinid monocots, silica bodies are present in all palms, Dasypogonaceae and Zingiberales
but present or absent in different taxa of Poales and Commelinales, with at least four separate
losses of silica bodies in Poales.
II. Introduction
Most plants have non-protoplasmic inclusions in some of their cells, such as calcium ox-
alate crystals, starch grains, tannins and silica bodies. In some groups the presence of such cell
inclusions may represent a potentially significant taxonomic character. For example, calcium
oxalate styloids are a characteristic feature of the family Iridaceae (Goldblatt et al., 1984; Rudall,
1994); also crystal druses are largely restricted to some basal monocotyledons: Acorus and
Alismatales (Prychid & Rudall, 1999, 2000; Keating, 2003). Silica bodies of various shapes
and sizes occur in leaves of several groups of monocotyledons, always in well-defined tissues.
This article reviews the presence, form and distribution of silica bodies in one large group of
flowering plants, the monocotyledons, in the context of both a historical review and a phyloge-
netic framework. Recent systematic analyses of monocotyledons that have considered this char-
acter have recorded only presence or absence of silica bodies. However, their form and position,
which are not greatly influenced by environmental factors but are clearly genetically controlled,
may also have considerable systematic potential.
Silica in the form of bodies or particles deposited within or on cells, as distinct from silica
incorporated in cell walls or completely filling hairs and other cells, occurs in certain groups
throughout the plant kingdom, including Selaginella (Bienfait et al., 1985; Le Coq et al., 1991),
Equisetum (Laroche, 1968; Kaufman et al., 1971), some ferns (Rolleri et al., 1987) and to a
small extent gymnosperm leaves and wood (Jiang & Zhou, 1989; Hodson et al., 1997; Sangster
et al., 1997), as well as some angiosperm families. Piperno (1988) listed pteridophytes, gymno-
sperms and angiosperms that contain silica bodies, with notes on their abundance and position.
Silica bodies may be found in all plant parts, although less commonly in roots. In wood they are
sometimes termed “silica grains” and are characteristically situated in the ray or axial paren-
chyma cells of certain genera in about 55 dicot families (see lists in Welle, 1976; Metcalfe &
Chalk, 1983; Espinoza de Pernía, 1987). In reproductive parts they may be different in shape
from those in vegetative parts, as Piperno (1989) showed in many tropical angiosperms.
III. Historical Review
The early history of this subject was well covered by Netolitzky (1929), but since his book
is not easily available a summary is given here. Davy (1814) was one of the first people to
investigate the form of silica in plants, including the epidermis of Triticum, Avena, Arundo and
Equisetum. Struve (1835) demonstrated for “tabaschir” in bamboo stems that silicified parts
remain intact after ashing but dissolve in caustic potash solution. Crüger (1857) found silica
bodies in Cauto bark (Moquilea or Hirtella species, Chrysobalanaceae) and Calamus paren-
chyma; he used both Schulze’s solution (nitric acid and potassium chloride) and a mixture of
sulphuric and chromic acids to isolate the silica, which he thought was always deposited in
dead cells. Von Mohl (1861) corroborated Crüger’s observations but disagreed with the
SILICA BODIES IN MONOCOTYLEDONS 379
hypothesis that silica deposition always occurs in dead cells. He found silica grains (reminis-
cent of starch grains) and silica filling entire cells in various plants and used hydrofluoric acid
to dissolve the silica and leave organic material. To obtain a silica skeleton he heated the mate-
rial in Schulze’s solution, then heated it in water and transferred it to alcohol before ashing in
a platinum crucible. Küster (1897) tested for silica with phenol, in which silica grains appear
reddish or bluish.
Wiesner (1867) distinguished short “silica cells” from long epidermal cells in Zea and Sac-
charum but thought they consisted of a wall thickening and silica incrustation; Wieler (1893,
1897) and Grob (1896) realized that the cell lumina are filled with silica. In Saccharum Wieler
(1893, 1897) showed that silicification proceeds inward from a silicified wall and eventually
fills the entire cell. The tiny cavities that are sometimes present in silica bodies of grasses were
thought to be remains of cytoplasm or gas bubbles (Frohnmeyer, 1914; Molisch, 1918).
Mettenius (1864) coined the terms “Deckzellen” (cover cells) or “Stegmata” (from the Greek
stegium, a roof or covering) for cells that contain inclusions and lie over sclerenchyma in ferns;
these cells enclosed calcium oxalate crystals in Cyatheaceae, silica concretions in Dryopteris
and true stegmata in most Trichomanes species. However, most subsequent authors have ap-
plied the term “stegmata” only to silica-containing cells. Rosanoff (1871) termed these silica
cells “Scheidenzellen” (sheath cells) because they often surround vascular bundles; he de-
scribed them in many orchids, palms, bamboos and Marantaceae, where they contain one or
sometimes two to three silica bodies per cell; the cells are often in axial files.
Pfitzer (1877) pointed out the positional homology between silica cells (stegmata) in or-
chids and crystal-containing cells in similar locations accompanying the vascular bundles in
many plants. Possession of either silica or calcium oxalate crystals in cells overlying vascular
bundles occurs frequently in plants; e.g., in ferns (crystals and/or silica), palms (silica: Molisch,
1913), Pandanaceae (crystals: Kohl, 1889), Xanthorrhoea (crystals: Rudall & Chase, 1996)
and Iridaceae (crystals: Goldblatt et al., 1984). Konstanty (1926) showed that files of crystal
cells, or so-called chambered crystal fibers, develop from division of parenchyma cells, not
fiber cells, and Netolitzky (1929) thought it likely that stegmata develop in a similar way.
Rosanoff (1871, translated from Russian of 1867) studied the development of such cells in the
root of Phoenix dactylifera and Syagrus botryophora; he observed that silica is laid down at a
very early stage in these cells, while they are still thin walled and contain cytoplasm. He did not
find any increase in number of the cells during development, although they are axially shorter
than adjacent sclerenchyma and parenchyma cells; he therefore concluded that in these species
the silica cells lose the capacity to grow and divide at an early stage.
Stegmata are characterized by a thickened wall adjacent to the underlying sclerenchyma
cells, with progressively thinner lateral walls and thin outer walls. The wall next to scleren-
chyma is often pitted, the pits corresponding to those of the sclerenchyma cell. Silica bodies in
stegmata may be spherical, conical, hat shaped or of intermediate type and may resemble crys-
tal druses (e.g., Ravenala, Strelitzia). The surface of the body is rarely completely smooth,
often spinulose or nodular or with a crater-like cavity (e.g., Musa). The thin outer walls of
stegmata often border large or small intercellular spaces.
The term “stegmata” is not normally applied to epidermal silica cells, even when they lie
over sclerenchyma associated with vascular bundles and possess the thickened inner periclinal
wall characteristic of stegmata, although Tomlinson (1969: 325) referred to “epidermal stegmata”
in Phenakospermum (Strelitziaceae). Epidermal silica cells frequently lie over sclerenchyma
fibers, either restricted to those accompanying vascular bundles as caps or girders or above
independent fiber strands. However, silica also occurs in intercostal cells, where it is often of a
different form from that in costal cells (e.g., many Cyperaceae and Poaceae).
380 THE BOTANICAL REVIEW
IV. Composition of Silica in Plants
Silica is an important component of many mineral soils and is the second most abundant ele-
ment in the Earth’s crust, after oxygen (Hodson & Evans, 1995). Soluble silica, the raw material of
silica body formation, is released into the soil by weathering of silicate minerals such as quartz and
feldspar (Piperno, 1988). For example, orthoclase feldspar, a mineral present in soil, is hydrolyzed
by the hydrogen and hydroxyl ions of water into the mineral kaolinite, resulting in the release of
potassium ions and monosilicic acid (Si(OH)
4
) into solution. Monosilicic acid is soluble in water
giving a concentration of ca. 2mM at 25ºC, higher concentrations implying that polymeric forms
of silica are present (Hodson & Evans, 1995). These latter two components are then taken up by
plant roots and transported throughout the plant in xylem sap.
4KAlSi3O8 + 4H+ + 18H2O Si4Al4O10(OH)8 + 4K+ + 8Si(OH)4
orthoclase feldspar kaolinite monosilicic acid
Minerals vary in their rates of weathering; for example, aluminosilicate clay minerals are more
susceptible to weathering than is quartz (Brady, 1990). There are two proposed mechanisms of
soluble silica uptake: active transport by metabolic processes or passive, nonselective flow in the
transpiration stream (Piperno, 1988). In plant tissues silicic acid becomes highly polymerized,
resulting in the deposition of solid, generally amorphous (non-crystalline) silicon dioxide
(SiO
2
.nH
2
O), either within or external to cells, often referred to as “opal” or “opaline silica” (Piperno,
1988). This process can occur at a very early stage of plant development, in almost any plant tissue.
Silica particles (ca. 10 nm in diameter) in mature hairs of the lemma of Phalaris canariensis may
be laid down in lines, thereby resembling rods, may form sheet-like arrangements of discrete par-
ticles or may be packed into disorganized arrays (Mann et al., 1983a, 1983b). Kaufman et al.
(1970) and Lawton (1980), working on Avena sativa and Lolium temulentum respectively, sug-
gested that the silica bodies in these species are made up of smaller silica rods that appear to grow
from the sides of the cell toward the center. In Oryza sativa, individual silica bodies each consist of
about 100,000 silica rods, each rod ca. 2.5
m long and 0.4
m wide (Dayanandan, 1983). The
silica particles in each rod have a diameter of 1–2 nm. Similarly, Jones et al. (1966) demonstrated
that silica in various taxa is composed of spherical particles up to 100 nm in diameter. On the other
hand, Hodson et al. (1984) cautioned that the spherical particles and the impression that the silica
had aggregated into rods could all be artifacts due to the sectioning of the material.
The water content of the silica ranges from 4% to 9%. Crystalline silicon phases have been
reported (Lanning, 1960; Sterling, 1967; Wilding & Drees, 1974), and it has been shown that
the composition of amorphous silica changes into a crystalline form as it ages (Wilding et al.,
1977). Silica bodies may also contain significant amounts of nitrogen and carbon, either within
the body itself or on its surface, possibly arising from cytoplasmic material, cellulose and/or
lignin. Other elements, such as aluminum, chlorine, copper, iron, manganese, phosphorous and
titanium, may also be present. Plant silica is optically isotropic, ranging in refractive index
from 1.41 to 1.47, has a specific gravity from 1.5 to 2.3 and, with a light microscope, ranges in
appearance from colorless or light brown to opaque (Jones & Beavers, 1963). Carbon pigmen-
tation may cause the darker forms of silica bodies. Frohnmeyer (1914) noticed that, in young
material of Saccharum officinarum, silica bodies are only weakly refractive.
V. Techniques
Several different techniques have been utilized to examine silica in plants, although light
microscopy is the primary method, often using standard anatomical methods of wax
SILICA BODIES IN MONOCOTYLEDONS 381
embedding and sectioning or epidermal peels (e.g., Frohnmeyer, 1914; Parry & Smithson, 1958;
Tomlinson, 1966; Blackman, 1969; Hodson & Sangster, 1988). Silica may be observed in situ
or extracted via various procedures, such as dry ashing under high temperatures (spodogram
technique: Parry & Smithson, 1958; Lanning et al., 1980). The ash may be assessed for silicon
dioxide content by difference of weights before and after treatment with hydrofluoric acid
(Lanning & Eleuterius, 1989). Wet ashing involves extraction by liquids, such as sulphuric
acid (Dayanandan, 1983), or digestion of organic material with nitric and perchloric acids
(Hayward & Parry, 1980). For example, Blackman (1971) made observations on silica mor-
phology in 26 species of grasses using either the spodogram technique or treatment with hydro-
gen peroxide and/or chromic acid. Parr et al. (2001) investigated a microwave digestion method
for the extraction of phytoliths from herbarium and/or fresh plant material without the need for
wet or dry ashing. They found that phytolith assemblages comparable to those of conventional
dry ashing were obtained quickly and without cross-contamination.
Localization of unstained and essentially transparent silica bodies using a light microscope
relies on differences in refractive indices between the mounting medium and silica (Parry &
Smithson, 1958; Dayanandan, 1983). However, there are a number of staining techniques. For
example, silica deposits (actually the silanol [SiOH] groups on the surfaces of silica particles),
may be localized by staining with silver-amine chromate, methyl red and crystal violet lactone
(Dayanandan, 1983). Sections may also be stained with phenol (Davis et al., 1973), any silica
present giving a magenta color reaction, and compared before and after treatment with hydro-
fluoric acid, which dissolves the silica (Gattuso et al., 1998). Anionic dyes may also be used to
visualize silica (Allingham et al., 1958). Total silica content may be determined colorimetri-
cally by a chemical process that results in the formation of a blue silica-molybdate complex
(Blackman, 1968; Yoshida et al., 1976; Gattuso et al., 1998).
Enzyme localization techniques were used by Blackman (1969) on developing silica cells
in the leaf sheath of wheat Triticum aestivum to look for metabolic peculiarities of potential and
developing silica cells. In addition to the greater level of succinic dehydrogenase activity found
in potential silica cells, the cells may contain substances with a specific activity related to silica
accumulation and precipitation or may even be manufacturing enzymes that will eventually
degrade the cell contents during silica body formation.
The scanning electron microscope (SEM) and image analysis systems have also been used
to evaluate and quantify variations in silica body morphological parameters and to investigate
distribution of silica deposits within tissues (Sangster, 1968; Hayward & Parry, 1980; Hodson
& Sangster, 1988; Rovner & Russ, 1992; Ball et al., 1993; Whang et al., 1998). Sophisticated
statistical programs can pick up significant differences between phytoliths produced in one
tissue type and those produced in another (Ball et al., 1993). Silica bodies sampled from a
single plant tissue may not necessarily be representative of those produced by the plant as a
whole. The SEM has also been used in conjunction with X-ray microanalysis to locate silica
and assess silica content (for reviews, see Parry et al., 1984; Harvey, 1986; Hodson & Sangster,
1989a, 1989b; Larcher et al., 1991; Dorweiler & Doebley, 1997; Gattuso et al., 1998). For
example, silica was localized in specific wall layers of the stomatal apparatus of sugarcane by
Sakai and Thom (1979). The technique relies on the production of a characteristic X-ray wave-
length for each element in the sample. If the wavelengths are recorded, they yield a list of the
elements present. Thus, images of only the areas producing a characteristic X-ray wavelength
are localizations of a particular element within the sample. Similarly, silica has been detected in
the leaves of various grasses using two analytical electron-microscopical techniques, Electron-
Energy-Loss-Spectroscopy (EELS) and Electron-Spectroscopic-Imaging (ESI) (Bode et al.,
1994). Brandenburg et al. (1985) visualized silica bodies in grass leaves using the SEM with
382 THE BOTANICAL REVIEW
backscattered electron imaging; previously this technique had mainly been used by materials
scientists and biomedical researchers. Hodson and Sangster (1989a) used this technique to
locate silica deposition in the inflorescence bracts of wheat (Triticum aestivum), and Whang et
al. (1998) studied the variation of epidermal silica bodies in rice (Oryza). The technique relies
upon the intensity of a backscattered electron signal being proportional to the average atomic
number of the sample irradiated, the higher the atomic number the brighter the signal. Areas of
high silica deposition would appear brighter on the image than areas of low silica deposition.
However, if other elements of higher atomic number, such as calcium, phosphorous, potas-
sium, sodium or sulphur, were also present in significant quantities these areas would also
appear bright and could thus be confused with the silica signal.
Wavelength dispersive electron probe microanalysis provides electron images of a speci-
men and also a corresponding X-ray distribution image for the particular element of interest.
Numerous studies have been carried out using this technique, including that of Sangster and
Parry (1976), who investigated the occurrence of silica in relation to endodermal thickening
and meristematic zones in Sorghum roots. Parry and Hodson (1982) and Parry et al. (1986)
mapped silica distribution in the caryopsis and inflorescence bracts of Setaria italica and leaves
of Bidens pilosa respectively, in relation to implications of plant silica in esophageal cancer.
Ultrastructural experiments using transmission electron microscopy (TEM) to examine up-
take of silicic acid and its subsequent incorporation into cell-wall silica were carried out by
Sowers and Thurston (1979). They grew Urtica pilulifera plants, which bear silicified stinging
cells on their leaves, in hydroponic solutions with and without supplements of silicic acid to
determine whether silicon starvation would affect plant growth. Ultrathin sections of plant
tissues were micrographed before and after treatment with hydrofluoric acid for comparison.
Similar experiments were undertaken by Chen and Lewin (1969) on Equisetum; they found
that successive reductions in available silicon in the growth solution resulted in an increasingly
stunted habit. Ultrastructural localization of soluble silicon has been carried out using freeze
substitution to preserve and embed specimen material (Ashton & Jones, 1976). This technique
reduces the loss of soluble components from the cells. Radioisotopes have been used in several
studies of silicon metabolism in higher plants as labels for silicic acid (Rothbuhr & Scott,
1957). Silica bodies or phytoliths that have been released into the soil through plant decay can
be radiocarbon-dated by utilizing the carbon trapped within the body. Amorphous silica gel has
very high X-ray absorptivities; Agarie et al. (1996) used soft X-ray analysis to determine silica
body distribution and relative frequency in whole leaves of Oryza sativa. Dried leaves were
irradiated with X rays on soft X-ray film; silica bodies appeared as black spots on the film.
Scanning transmission electron microscopy (STEM) has also been used (Hodson et al.,
1984; Hodson & Sangster, 1993) to localize silica. For instance, Hodson and Sangster (1993)
used the technique to look at the interaction between silicon and aluminum in the freeze-dried
roots of Sorghum bicolor. The higher resolution of the STEM meant that the authors could
localize the aluminum/silicon deposit of the root epidermis to the outer tangential wall.
VI. Uptake and Deposition
Lewin and Reismann (1969) and Raven (1983) reviewed the evidence for passive uptake of
monosilicic acid in certain plants. A mechanism of this type would allow prediction of the
amount of deposited silicon in a plant from the concentration of silicic acid in the growth
medium, as Jones and Handreck (1965) inferred in oat plants. However, there is also evidence
for active uptake of soluble silica in some species. For example, in rice shoots, silicic acid can
pass into xylem sap even against a concentration gradient (Okuda & Takahashi, 1964). Hodson
SILICA BODIES IN MONOCOTYLEDONS 383
and Evans (1995) found that more silica is taken up by wetland grasses than would be predicted
from the quantity of silica present in the soil solution and the transpiration rate, thereby imply-
ing an active uptake mechanism. Piperno (1988) suggested that both active and passive absorp-
tion may occur in different species or even, sometimes, in different regions of the same plant.
Silica accumulation (sensu Takahashi & Miyake, 1977) is characteristic of some plant fami-
lies, whereas others produce little or no silica. Species with little silica control the amount of
silicic acid that enters the root or passes from the root to the aerial tissues of the plants (Piperno,
1988). Jones and Handreck (1969) proposed a hypothetical barrier in root epidermal cells of
clover (Trifolium incarnatum) that restricted the flow of silicic acid into the transpiration stream.
Experiments undertaken by Parry and Winslow (1977) on pea seedlings (Pisum sativum) showed
that there is some mechanism at the root surface which disallows the passage of monosilicic
acid into the root. In other species, such as Vicia fabia and Ricinus communis, a layer of fatty
substance on the root-hair surface may form the barrier (Parry & Winslow, 1977).
In monocotyledons, relatively few studies on opaline silica bodies have considered devel-
opmental aspects, especially using modern methods. Grob (1896), Frohnmeyer (1914) and
Prat (1931) examined silica deposition in Poaceae. They found differing types, ranging from a
fine-grained silica network, with accumulating silica continuing to fill the cell centripetally
(Grob, 1896), to the formation of a “silica ring” around the cell periphery enclosing the cell
contents, which later increases, restricting the cell lumen (Frohnmeyer, 1914). Mature silica
bodies have characteristic vesicular cavities within them; Grob (1896) related the position of
these cavities to the stage of silica deposition. In Saccharum officinarum, silica deposition
occurs rapidly, and there is layering or stratification in the peripheral silica (Blackman, 1969).
Frohnmeyer (1914) suggested that rapid deposition of silica results in homogeneous silica
bodies, whereas slow deposition results in non-homogeneous silica masses. In Arundo donax a
thin silica ring is formed around the periphery of the cell, and the cell lumen is then filled either
by formation of a fine network or by growth of a silica ring, a form of deposition intermediate
between the two previous types. Silica may also be deposited on a dispersed organic matrix
within the cell, since broken silica bodies have a porous internal structure (Grob, 1896; Sangster,
1968). Prat (1931) suggested that transparent silica bodies originate from an opaque silica gel
stage and that granular inclusions within them are the remains of the nucleus and cytoplasmic
contents. In addition to infillings of the cell lumen, silica may also be laid down as deposits
within the cell wall or between the cellulose wall and the plasma membrane (cell-wall deposi-
tion or membrane silicification: Drum, 1968), or in cortical intercellular spaces (Montgomery
& Parry, 1979). Cell-wall incrustations are common in dicotyledons, whereas infilling of the
cell lumen occurs more frequently in monocotyledons (Piperno, 1988).
Developing silica cells in the leaf sheath of wheat (Triticum aestivum) have an apparently
normal cuticle but differ from surrounding cells in having smaller nucleoli and thinner outer
cellulose walls (Blackman, 1969). Thin outer cellulose walls may result in a higher rate of
transpiration, facilitating an influx of silica as monosilicic acid. Jones and Handreck (1967),
Sangster and Parry (1971) and Raven (1983) all cited transpiration or water loss as a major
factor in silica polymerization. In some species, greater amounts of silica are deposited in those
regions of the plant where water loss is highest. However, this is not always the case, since
silica is often deposited in tissues that restrict water loss, such as sclerenchyma. Indeed, the
association between development of silica bodies and sclerenchyma requires further explora-
tion, since the two are often associated; for example, in orchids (Møller & Rasmussen, 1984).
Parry et al. (1984) considered that a passive, transpiration-based process cannot account for
many cases of localized silica deposition. Such highly localized silica distribution patterns
indicate genetic control that is phylogenetically mediated.
384 THE BOTANICAL REVIEW
Nuclei and other cell contents degenerate before silica bodies are formed, resulting in “empty”
cells possessing no apparent cell contents or silica bodies. The small size and rapid degenera-
tion of nuclei indicate that protein synthesis in the cell is at a minimum (Lowary & Avers,
1965). As the concentration of monosilicic acid in the cell increases, the solution becomes
supersaturated, changing to a sol form and then to a highly polymerized gel (SiO2.nH2O). This
process could result from a reduction in cellular pH to 5.0–6.0, probably caused by the break-
down of the cellular buffering system as the cytoplasm degenerates (Iler, 1955). The polymer-
ization and gelling processes may also be catalyzed by the presence of organic molecules. The
mechanism of silica deposition is also thought to involve other mineral ions (Perry et al.,
1984a, 1984b; Hodson & Bell, 1986). Often the polymerized silicic acid fills the cell lumen
and binds to the cellulose cell walls, forming a silico-cellulose membrane; thus cell walls can
be silicified (Lewin & Reismann, 1969; Schwarz, 1973). The increasing concentration of silica
in the cell results in highly refractive mature silica bodies that typically fill the whole cell
(Blackman, 1969).
The genetic control of silica deposition is also under investigation. For example, a single
Mendelian locus located on maize chromosome 4, teosinte glume architecture 1 (tga1), has a
major influence on several aspects of cupulate fruit-wall morphology, both in maize (Zea mays
ssp. mays)
and its wild progenitor, teosinte (Zea mays ssp. parviglumis). Dorweiler and Doebley
(1997) demonstrated that the teosinte allele (tga1 + teosinte) increases cellular deposition of silica.
They suggested that tga1 regulates which cells of the glume and rachis epidermis become
silicified, since it apparently activates silica deposition in certain cells or represses it in others.
VII. Morphology and Location
There are several morphological forms of silica in monocot tissues, and the number of silica
bodies per cell may also vary. Classification of phytoliths is invariably based on their sizes and
shapes; for example, Bertoldi de Pomar (1971) proposed two morphological groups:
microsilicophytoliths and macrosilicophytoliths. The most common type of silica body in mono-
cots is the “druse-like” spherical, spherical-rugose (nodular) or spherical-spinulose type, usu-
ally a single body per cell but sometimes more. Other forms include the “hat-shaped” type
(sometimes called a “truncated conical”), trough-shaped and an amorphous, fragmentary type
(silica sand). These shapes are consistent enough within genera or tribes to be used as charac-
ters in taxonomic studies (e.g., Stebbins, 1956; Metcalfe, 1960) and as an aid in identification
(e.g., Wilding & Drees, 1968; Dormaar & Lutwick, 1969; Lutwick & Johnston, 1969; Twiss et
al., 1969).
Another variable feature is the relative location of silica bodies in plant tissues. They are
most commonly found either in the epidermis (e.g., in grasses, commelinas and sedges) or in
the sheath cells of vascular bundles (e.g., in palms, bananas and orchids). Silica-bearing cells
are most commonly associated with sclerenchyma, either subepidermal sclerenchyma (in the
case of epidermal silica) or bundle-sheath sclerenchyma, although there are exceptions to this.
VIII. Ecology
A number of ecological factors, including climate, soil variability, moisture availability and
plant age, affect silica body development by regulating the concentrations of dissolved silica
that is available to plants (for a review, see Piperno, 1988). In many species, leaves of older
plants contain greater amounts of silica than do their younger counterparts, possibly due in part
to cellular changes required to obtain silica and in part to an increased availability of deposition
sites (Bezeau et al., 1966; Blackman, 1968, 1969; Lanning & Eleuterius, 1985). In some
SILICA BODIES IN MONOCOTYLEDONS 385
species, an increase in the amount of dissolved silica in a growth medium increases the amount
of plant silica (measured as a percentage of dry weight) in direct proportion (Okuda & Takahashi,
1961; Jones & Handreck, 1965). Weathering of silicate minerals is thought to be accelerated by
wet climates, thereby liberating greater quantities of soluble silica into the soil than in dry
climates (Dunne, 1978), partly explaining the relatively greater concentrations of silica in wet
tropical soils (Siever, 1967). Tropical plant root systems are extremely efficient in absorbing
any soil nutrients present, resulting in high concentrations of silica in these plants (Lovering,
1959; Riquier, 1960; Piperno, 1985).
Plants of the same species grown in different soils can contain different amounts of silica.
Substances such as iron and aluminum oxides, which may be present in the soil, are known to
interact with silica under appropriate conditions, producing colloidal complexes that are not
taken up by biological systems (Birchall, 1990; Exley & Birchall, 1992, 1993), t
hereby reduc-
ing the amount of soluble silica available. Indeed, the amount of aluminum and silica that plants
transport in their tissues varies considerably, and there is some evidence that very high aluminum
accumulation and very high silica accumulation are mutually exclusive (Hodson & Evans, 1995).
Exley and Birchall (1993) postulated that silicic acid inhibits the nucleation of aluminum hydrox-
ide by forming hydroxyaluminosilicate complexes and that this process was found to increase with
increasing pH.
Independent of these substances, soluble silica concentration has been shown to
reach a maximum at a soil pH of 8–9 (McKeague & Cline, 1963), with the result that more
soluble silica is available to plants growing in acid soils. However, silica solubility rises con-
siderably above pH 9.0 due to silicate ion formation (Hodson & Evans, 1995).
Increased soil water content may result in increased silica uptake (Jones & Handreck, 1967).
For example, grasses grown in the floodwater fields of Egypt had greater silica deposition than
did grasses grown in areas where rainfall agriculture was practiced (Miller, 1980). T
he amount
of solid silica in the plant decreases when high concentrations of nitrogen and phosphorus are
present in the soil. Soluble silica also increases with an increase in the amount of decomposed
organic material in the soil. On the other hand, silica bodies are often present in epiphytic orchids,
which do not have access to soluble silica in groundwater but instead obtain it from rainwater.
Terrestrial orchid species often lack silica (see section XI, “Systematic Distribution”).
Although silica uptake and concentration are affected by environmental factors, they are
primarily under genetic control (Piperno, 1988). Families considered to be non-accumulators
do not accumulate silica regardless of the environmental conditions. Plants that show different
morphological forms of silica retain their individual silica morphologies when grown under
identical environmental conditions.
IX. Functions
Silica is considered to be an important factor for normal growth and development (Agarie et
al., 1996). The study of silicon metabolism is beyond the scope of the present review. We are
concerned here with deposits of silica, which have sometimes been regarded as a waste product
or as a form of storage, from which silicon can be mobilized if needed to interact with other
elements; e.g., aluminum (Hodson & Evans, 1995). It has been suggested that epidermal silica
bodies may act to reduce transpiration in leaves (Yoshida, 1965; Lanning & Eleuterius, 1983),
thereby improving water use efficiency (Yoshida et al., 1959). Hutton and Norrish (1974) found
a direct correlation between the silicon percentage in wheat husks and the quantity of water
transpired.
The “window” hypothesis postulated that the presence of epidermal silica bodies facilitates
the transmission of light through the epidermis to the photosynthetic mesophyll or to stem
cortical tissue, consequently increasing photosynthesis and plant growth (e.g., Takeoka et al.,
386 THE BOTANICAL REVIEW
1979). However, Kaufman et al.’s (1979, 1981, 1985) investigations did not support the sug-
gestion, and Agarie et al. (1996) disproved this hypothesis in rice.
Silica may help to maintain rigidity in stems and linear leaves, although leaf stiffness may
also be related to the degree of lignification (Matsuda et al., 1983). Silica has been shown to
improve lodging resistance in wheat (Gartner et al., 1984).
Silica content may be related to grazing of grasses by herbivores (Vicari & Bazely, 1993).
McNaughton and Tarrants (1983) and McNaughton et al. (1985) found that silica content was
higher in heavily grazed grasslands than in others and that more silica was present in plant
tissues produced early in the growing season. In a feeding experiment, prairie voles (Microtus
ochrogaster) preferentially ate grasses with low silica content (Gali Muhtasib et al., 1992).
Wadham and Parry (1981) investigated the relationship between silica content and slug resis-
tance.
Djamin and Pathak (1967) tested several rice varieties and found that those with high silica
content showed greater resistance to Asiatic stem borer (Chilo suppressalis) than others, prob-
ably because the silica interfered with boring and feeding of the larvae; selecting rice varieties
with a high silica content was more economical than applying silicate to the soil. Hanifa et al.
(1974) studied the role of silica in the resistance of rice to the leaf roller (Cnaphalocrocis
medinalis), and Moore (1984) examined the relationship of silica to stem-borer infection by
Oscinella species in Lolium.
Silica body content may be correlated with resistance to fungal diseases; for instance, brown
spot disease of rice (Nanda & Gangopadhyay, 1984) and blast disease of rice (Suzuki, 1937).
X. Applications
A. SOILS AND ARCHAEOLOGY
Silica bodies and other silicified plant parts, such as silicified hairs and cell walls, occurring
in soils, dust, etc., are termed “phytoliths,” or sometimes “silicophytoliths,” “opal phytoliths”
or “plant opal.” The term “phytolith” may also be applied to other mineral structures of plant
origin, such as calcium oxalate crystals, but is more usually restricted to silica particles. Deflandre
(1963) reported that Ehrenberg (1841) was one of the first scientists to recognize that these
particles were, at least in part, of plant origin; Ehrenberg studied them in soils and classified
them by shape, terming them “phytolitharia.” The study of phytoliths in soils and archaeologi-
cal material has proved a valuable aid for determining vegetation types in a particular locality
at various ages in the past and thus reconstructing palaeoenvironments, as well as for investi-
gating ancient agricultural practices and crop-plant evolution. Phytoliths are extremely durable
in soil and may not migrate through it to the same extent as do other microfossils, such as
pollen and diatoms. However, while phytoliths derived from grasses and sedges may be abun-
dant, those from some vegetation types may be underrepresented or absent; for example, gym-
nosperms and ferns (Horrocks et al., 2000).
This is a vast subject, and we refer the reader to relevant texts for more information (Rovner,
1986; Piperno, 1988; Mulholland, 1989; Pearsall, 1989; Rapp & Mulholland, 1992; Wang &
Lu, 1993; Pinilla et al., 1997). As an example of this work, we can cite Blinnikov (1994), who
found different phytolith assemblages in changing alpine plant communities in the northwest-
ern Caucasus, and Madella (1997), who analyzed the phytolith content of sediments from mod-
ern and palaeosols in Tadjikistan and was able to show that at certain periods grasses
predominated, whereas at others there were also gymnosperms and dicot trees in the vegeta-
tion. Runge and Runge (1997) demonstrated rain-forest degradation and vegetation changes in
East Africa by examination of phytoliths in sediments and comparison with those extracted
SILICA BODIES IN MONOCOTYLEDONS 387
from species composing different present-day plant communities. Changes in forest and grass-
land vegetation in Arizona were examined by Kerns et al. (2001) and Kerns (2001) and in
Washington State by Blinnikov et al. (2002). The spread of grasslands in the Late Tertiary of
Nebraska was investigated by Stromberg (2002). Such studies rely on a comprehensive refer-
ence collection of plants from the area of study, as has been provided by Palmer and others for
East African grasses (Stewart, 1965; Palmer & Tucker, 1981, 1983; Palmer et al., 1985; Palmer
& Gerberth Jones, 1986, 1988), Brown (1984), Mulholland (1989), Fredlund and Tieszen (1994)
and Piperno and Pearsall (1998) for the USA, and Kealhofer and Piperno (1998) for the South-
east Asian flora.
Archaeological studies are very varied, ranging from analysis of the phytoliths or wear
associated with prehistoric or recent human (Puech et al., 1983; Lalueza et al., 1996; Cummings
& Magennis, 1997; Juan-Tresserras et al., 1997; Gugel et al., 2001) or animal (Baker et al.,
1959; Armitage, 1975; Acuna-Mesen & Garcia-Diaz, 1998) teeth and the information they
provide about diet to investigations of ancient settlements (e.g., Kajale & Eksambekar, 1997)
and basketry (Ollendorf et al., 1988). Rosen (1992) demonstrated that it was possible to distin-
guish between cereal straw and husks in archaeological settlements by the use of silica skel-
etons of epidermal cells.
The occurrence of palm remains, including phytoliths, at New World archaeological sites
provides evidence for palm dispersal by humans (Morcote-Ríos & Bernal, 2001). Stegmata in
fossil palm stems have been demonstrated by Ancibor (1995).
B. AGRICULTURAL CROPS AND THEIR EVOLUTION
An important field of research deals with changes in agricultural practices over time and
with ancient crop plants and their evolution. There is a large body of literature on maize (e.g.,
Piperno, 1988; Bush et al., 1989; Russ & Rovner, 1989; Pearsall & Piperno, 1990; Doolittle &
Frederick, 1991; Bozarth, 1993; Piperno & Pearsall, 1993; Dorweiler & Doebley, 1997; Piperno
& Flannery, 2001), rice (Fujiwara & Sasaki, 1978; Fujiwara et al., 1990; Sato et al., 1990;
Udatsu & Fujiwara, 1993; Cailin et al., 1994; Pearsall et al., 1995; Whang et al., 1998; Zhao et
al., 1998; Huang & Zhang, 2000) and wheat (Ball et al., 1993). Musa phytoliths (distinguished
from Ensete) have been found in refuse pits dated to the first millennium B.C. in Cameroon and
provide evidence for early banana cultivation and contacts with Asia, where Musa is native
(Mbida Mindzie et al., 2001); edible bananas do not produce pollen or seeds, so in this case
phytolith evidence is particularly useful.
C. MEDICAL STUDIES
The identification of drug plants may be aided by the study of phytoliths (Umemoto &
Hozumi, 1971a, 1971b; Umemoto et al., 1973). Silica particles in dust from plant fragments in
the atmosphere have been found to affect the health of workers (Baker, 1961; Hodson & Sangster,
1988, 1989a), while silicified particles in cereal foods have been implicated in causing esoph-
ageal cancer (Bennett & Parry, 1981; Hodson et al., 1982; O’Neill et al., 1982, 1986; Parry &
Hodson, 1982; Newman & Mackay, 1983; Sangster et al., 1983). Silica of plant origin was
reported in human intestines as long as 150 years ago (Quekett, 1852), and it may be the cause
of urinary complaints in cattle (Bezeau et al., 1966) and sheep (Baker et al., 1961).
D. ANIMAL DIETS
Analysis of phytoliths from teeth or in the digestive system or feces has been used to help
determine the diet of herbivorous mammals (Baker et al., 1961; Cherouvrier et al., 1975; Chapuis,
388 THE BOTANICAL REVIEW
1980), insects (Gueguen et al., 1975) and snails (Chevalier et al., 2001). It may even be used to
study the diet of extinct species such as the moa (Kondo et al., 1994) and American mastodon
(Gobetz & Bozarth, 2001). The digestibility of animal foodstuffs may be related to the silica
content (Van Soest & Jones, 1968; Harbers et al., 1981; Balasta et al., 1989).
E. OTHER APPLICATIONS
Comparison of phytolith assemblages in soils from different sites may be useful in forensic
investigations (Marumo & Yanai, 1986). Silica extracted from plants has been used in the
construction of solar cells (Amick, 1982). Rice husks have been utilized in the manufacture of
composite board (Côté, 1974) and as a filler to enhance properties of natural rubber vulcanizates
(Sae-Oui et al., 2002). The silica extracted from rice husks has been tested for use in high-
performance concrete (Chandrasekhar et al., 2002) and as a filler in epoxy resin for embedding
material in electronic devices (Suwanprateeb & Hatthapanit, 2002).
XI. Systematic Distribution
Recent analyses of molecular sequence data (e.g., Chase et al., 2000; Stevenson et al., 2000)
have identified several well-supported major monocot clades. However, even combined
multigene analyses (e.g., Chase et al., 2000) have yielded an unresolved polytomy between six
of these clades (perhaps representing a relatively deep, rapid radiation): the four lilioid orders
(Asparagales, Liliales, Dioscoreales and Pandanales), the large commelinid clade and the small
bigeneric family Petrosaviaceae (Fig. 1). The major clades can be grouped for convenience
into: 1) basal monocots (Acorus and Alismatales); 2) a polyphyletic assemblage of five clades
of lilioid monocots (Asparagales, Liliales, Dioscoreales, Pandanales and Petrosaviaceae); and
3) a monophyletic group encompassing all the commelinid monocots, including bromeliads,
grasses, sedges, rushes, palms and gingers (Fig. 1). Silica bodies are not found in basal mono-
cots or lilioid monocots (apparent reports are based on confusion with crystals); with the single
exception of the asparagoid family Orchidaceae, which are thus the only non-commelinid mono-
cots with silica bodies (Table I).
Fig. 1. Generalized diagram of monocot relationships based on Chase et al. (2000), showing silica
distribution.
SILICA BODIES IN MONOCOTYLEDONS 389
Table I
Distribution of silica bodies in families of monocotyledons
Order, family Silica bodies
Basal monocots
Acoraceae Absent
Alismatales
Araceae, Alismataceae, Aponogetonaceae, Butomaceae,
Cymodoceaceae, Hydrocharitaceae, Juncaginaceae,
Lilaeaceae, Limnocharitaceae, Najadaceae, Potamogetona-
ceae, Scheuchzeriaceae, Tofieldiaceae, Zannichelliaceae,
Zosteraceae
Absent
Lilioid monocots
Petrosaviaceae
Pandanales
Cyclanthaceae, Pandanaceae, Stemonaceae, Triuridaceae,
Velloziaceae
Absent
Dioscoreales
Burmanniaceae (incl. Thismiaceae), Dioscoreaceae (incl.
Stenomeridaceae, Taccaceae, Trichopodaceae), Nartheciaceae
Absent
Asparagales
Higher asparagoids: Agapanthaceae, Agavaceae, Alliaceae,
Amaryllidaceae, Anemarrhenaceae, Anthericaceae, Aphyl-
lanthaceae, Asparagaceae, Behniaceae, Hyacinthaceae, Lax-
manniaceae, Ruscaceae (incl. Eriospermaceae,
Convallariaceae, Dracaenaceae, Nolinaceae), Themidaceae
Absent
Lower asparagoids: Asphodelaceae, Asteliaceae, Blandfordi-
aceae, Boryaceae, Doryanthaceae, Hypoxidaceae, Iridaceae,
Ixioliriaceae, Lanariaceae, Tecophilaeaceae, Xanthorrhoea-
ceae, Xeronemataceae
Absent
Orchidaceae Present or absent (Table II)
Liliales
Alstroemeriaceae, Campynemataceae, Corsiaceae, Colchicaceae,
Liliaceae, Luzuriagaceae, Melanthiaceae, Philesiaceae, Smila-
caceae
Absent
Commelinid monocots
Arecaceae (Palmae) (c. 190 genera, 2000 spp.) Present (Table III)
Dasypogonaceae (4 genera, 8 spp.) Present (Table X)
Hanguanaceae (1 genus, 5+ spp.) Present (Table IV)
Commelinales
Commelinaceae (incl. Cartonemataceae) (2 subfamilies, 4 tribes,
41 genera, 650 spp.)
Present or absent (Table IV)
Haemodoraceae (2 subfamilies, 13 genera, 100 spp.) Present or absent (Table IV)
Philydraceae (4 genera, 5 spp.) Absent
Pontederiaceae (9 genera, 33 spp.) Absent
Poales
Anarthriaceae (1 genus, 7 spp.) Absent
Bromeliaceae (56 genera, 2600+ spp.) Present (Table VI)
Centrolepidaceae (3 genera, 35 spp.) Present or absent (Table VI)
Cyperaceae (104 genera, 5000+ spp.) Present (Table IX)
Ecdeiocoleaceae (2 genera, 2 spp.) Present (Table VI)
Eriocaulaceae (10 genera, 700–1400 spp.) Absent
Flagellariaceae (1 genus, 4 spp.) Present (Table VI)
Hydatellaceae (2 genera, 10 spp.) Absent
Joinvilleaceae (1 genus, 2 spp.) Present (Table VI)
390 THE BOTANICAL REVIEW
Recent molecular analyses have found Orchidaceae to be monophyletic and placed in the
order Asparagales (sensu APG, 1998), either as the sole sister taxon to all other Asparagales
(Fay et al., 2000) or as sister to the earliest-diverging clade of Asparagales (in analyses of rbcL
alone: e.g., Chase et al., 1995a; Rudall et al., 1997), although they are at best weakly supported
in these positions. On present phylogenetic evidence, the presence of silica bodies in both
commelinids and orchids in contrast to all other monocots must therefore be interpreted as a
homoplasy; i.e., de novo development of silica bodies in two closely related taxa, as Møller and
Rasmussen (1984) suggested. This homoplasy may be adaptive, as a result of similar environ-
mental constraints, or it could have resulted from an iterative gene mutation at a time of rapid
monocot radiation. Silica body structure and distribution within tissues are closely similar in
orchids and putatively “basal” commelinids such as palms. Evolutionary events, such as a
secondary loss of silica bodies in some groups and their apparent regain in others, presumably
reflect underlying differences in cell chemistry.
A. ORCHIDACEAE
The most widely used orchid classification is still that of Dressler (1993). However, even
this classification requires some revision following a recent analysis of molecular data from
rbcL (Cameron et al., 1999) that produced five major orchid clades, roughly corresponding to
the five traditional subfamilies Epidendroideae (including Vandeae, Dendrobieae, Neottieae
and other tribes), Orchidoideae (including Diurideae, Cranichideae, Diseae and Spirantheae),
Vanilloideae, Cypripedioideae and Apostasioideae. Subfamilies Apostasioideae, Vanilloideae
and Cypripedioideae are all relatively poor in numbers of genera and species. Most of the
taxonomic diversity in orchids is encompassed by Orchidoideae and especially Epidendroideae.
The bigeneric subfamily Apostasioideae (Apostasia and Neuwiedia) is traditionally regarded
as the sister group to other orchids (reviewed by Dressler, 1993). Furthermore, all of the most
recent molecular and morphological analyses support this basal position (Cameron et al., 1999;
Freudenstein & Rasmussen, 1999; Cameron & Chase, 2000; Freudenstein et al., 2000).
Table I, continued
Order, family Silica bodies
Commelinid monocots, continued
Poales, continued
Juncaceae (8 genera, 350 spp.) Present or absent (Table VI)
Mayacaceae (1 genus, 4–10 spp.) Absent
Poaceae (Gramineae) (700+ genera, 10,000+ spp.) Present (Table VI)
Rapateaceae (16 genera; 80 spp.) Present (Table IX)
Restionaceae (55 genera; 490 spp.) Present (Table VII)
Thurniaceae (1 genus; 3 spp.) Present (Table VI)
Typhaceae (incl. Sparganiaceae) (2 genera; 16–30 spp.) Absent
Xyridaceae (5 genera; 300 spp.) Absent
Zingiberales
Cannaceae (1 genus, 25 spp.) Present (Table V)
Costaceae (4 genera, 100 spp.) Present (Table V)
Heliconiaceae (1 genus, 200 spp.) Present (Table V)
Lowiaceae (1 genus, 10 spp.) Present (Table V)
Marantaceae (31 genera, 550 spp.) Present (Table V)
Musaceae (2 genera, 40 spp.) Present (Table V)
Strelitziaceae (3 genera, 7 spp.) Present (Table V)
Zingiberaceae (50 genera, 1300 spp.) Present (Table V)
SILICA BODIES IN MONOCOTYLEDONS 391
Following Apostasioideae, the next-branching orchid subfamily is either Cypripedioideae or
Vanilloideae (cf. Cameron et al., 1999; Pridgeon et al., 2001; Cameron & Chase, 2000; Molvray
et al., 2000; K. Cameron, pers. comm., 2001).
Møller and Rasmussen (1984) reviewed early work on silica bodies in orchids and added
many original observations. In orchids, silica bodies occur in stegmata overlying sclerenchy-
matous vascular bundle sheaths, especially adjacent to the phloem, or over independent fiber
strands in leaves and stems (including rhizomes and pseudobulbs), absent from the epidermis,
although they may be subepidermal. In the leaf of a few Maxillaria species silica cells have
been recorded in hypodermal or chlorenchyma cells independent of sclerenchyma (Davies,
1999). In stems the stegmata are on the outer surface of a sclerenchyma ring, in which vascular
bundles may be embedded, or in connection with vascular bundles scattered in the ground
tissue. The only reports for roots are in three Cymbidium spp. (Cyrtopodiinae) (Yukawa &
Stern, 2002), one Maxillaria sp. (Maxillariinae) and a few species of Lycastinae (Holtzmeier et
al., 1998; Yukawa & Stern, 2002). Interestingly, Cameron et al. (1999) suggested that tribes
Cymbidieae and Maxillarieae may be closely related, based on rbcL sequence data, and Yukawa
& Stern (2002) considered that root stegmata might be a synapomorphy in the Cymbidieae-
Maxillarieae clade.
Silica bodies are entirely absent from two orchid subfamilies, Vanilloideae and Orchidoideae
(Table II). In Cypripedioideae they are either conical, rod-like or absent. Silica bodies are also
absent from most tribes or subtribes of Epidendroideae but present in Apostasioideae, which
are the putative sister group to all other Orchidaceae. The most parsimonious interpretation is
therefore that silica bodies are secondarily lost in groups that lack them entirely. The alternative
would require multiple origins of silica bodies within orchids, which seems less plausible. In
some (but by no means all) of the subtribes lacking silica bodies, sclerenchyma is also absent
(Møller & Rasmussen, 1984).
Orchid stegmata are small cells that are usually arranged in continuous or discontinuous
axial files; in some cases a file may border one axially elongated air canal. There is generally
one silica body per cell. Silica bodies are of two types in orchids: 1) conical or hat shaped,
sometimes spiny (Fig. 2A), or 2) spherical, often with a rough, warty or spiny surface (Fig. 2B).
The conical type is by far the most common in orchids. Silica and crystals frequently occur in
the same plant. Spherical silica bodies are restricted to three groups within orchids, one species
of Apostasioideae (see below) and two groups of Epidendroideae: 1) subtribes Eriinae,
Podochilinae and Dendrobiinae of tribe Podochileae, and 2) all three subtribes of Vandeae. In
a few of these groups conical bodies also occur occasionally, but the only group in which
Møller and Rasmussen (1984) recorded both conical and spherical types was Podochilinae, in
which Agrostophyllum had conical bodies and the other two genera examined had spherical
ones. However, Agrostophyllum has since been transferred to Glomerinae in Dressler’s system,
in which all the genera have conical silica bodies. Yan Peng Ng (pers. comm., 2000) also
reported records of both conical and spherical silica bodies in the large and possibly polyphyl-
etic genus Eria. Møller and Rasmussen (1984) and Rasmussen (1986) noted that spherical
bodies occur only in epiphytic orchids, whereas conical ones are present in both epiphytic and
terrestrial species. They suggested that the conical type and terrestrial state might be ancestral
and that spherical bodies might have evolved at least twice. Given our current knowledge of the
phylogenetic distribution of the two types in orchids, their assessment is certainly possible,
despite the fact that in commelinids the spherical type is apparently the plesiomorphic condi-
tion. However, the putatively basal subfamily Apostasioideae is interesting in this context be-
cause the single orchid species so far known to possess both conical and spherical bodies is
Apostasia wallichii, which has spiny conical bodies in the leaf and spiny spherical bodies in the
(Text continues on p. 397)
392 THE BOTANICAL REVIEW
Table II
Distribution of silica bodies in Orchidaceae (classification of Dressler, 1993).
Key to location: L = leaf; R = root;S=stem(including rhizome and pseudobulb. Key to type: C = conical; Sph = spherical; Abs = absent.
Brackets indicate few seen or variable.
Subfamily, tribe, subtribe
No. of
genera
No.
studied
Location /
organs
studied Type Notes References
Apostasioideae 2 2 L, S L: C; S: Sph, C, Abs C (L) & Sph (S) in
1 sp. (Stern et al.)
Møller & Rasmussen, 1984; Stern et al., 1993a
Cypripedioideae 4 3 L (C), (rod), Abs Solereder & Meyer, 1930; Møller & Rasmussen,
1984
Spiranthoideae
Diceratosteleae 1 1 L, S C Stern et al., 1993b
Tropidieae 2 2 L, S C Møller & Rasmussen, 1984; Stern et al., 1993b
Cranichideae
Goodyerinae 35 13 L, S Abs Møller & Rasmussen, 1984; Stern et al., 1993b
Prescottiinae 7 2 L, S Abs Møller & Rasmussen, 1984; Stern et al., 1993b
Spiranthinae 41 6 L, S Abs Møller & Rasmussen, 1984; Stern et al., 1993b
Manniellinae 1 1 L Abs Stern et al., 1993b
Pachyplectroninae 1 1 L Abs Stern et al., 1993b
Cranichidinae 9 2 L Abs Møller & Rasmussen, 1984; Stern et al., 1993b
Orchidoideae
Diurideae
Chloraeinae 6 1 L Abs Møller & Rasmussen, 1984
Caladeniinae 10 9 L Abs Pridgeon, 1994
Drakaeinae 5 5 L Abs Møller & Rasmussen, 1984; Pridgeon, 1994
Pterostylidinae 1 1 L Abs Møller & Rasmussen, 1984
Acianthinae 5 1 L Abs Møller & Rasmussen, 1984
Cryptostylidinae 2 1 L, S Abs Stern et al., 1993b
SILICA BODIES IN MONOCOTYLEDONS 393
Diuridinae 3 –
Thelymitrinae 2 1 L Abs Møller & Rasmussen, 1984
Rhizanthellinae 1 –
Prasophyllinae 3 1 L Abs Møller & Rasmussen, 1984
Orchideae
Orchidinae 35 13 L, S, R Abs Kohl, 1889; Solereder & Meyer, 1930; Møller &
Rasmussen, 1984; Stern, 1997a
Habenariinae 24 4 L, S, R Abs Møller & Rasmussen, 1984; Stern, 1997b
Diseae
Huttonaeinae 1 1 L, S Abs Kurzweil et al., 1995
Satyriinae 3 3 L, S Abs Møller & Rasmussen, 1984; Kurzweil et al., 1995
Coryciinae 5 4 L, S Abs Møller & Rasmussen, 1984; Kurzweil et al., 1995
Disinae 5 5 L, S Abs Møller & Rasmussen, 1984; Kurzweil et al., 1995
Epidendroideae
Neottieae
Limodorinae 4 2 L C, Abs C in 1 sp. Kohl, 1889; Molisch, 1920; Solereder & Meyer,
1930; Møller & Rasmussen, 1984
Listerinae 2 2 L Abs Kohl, 1889; Solereder & Meyer, 1930
Palmorchideae 1 –
Triphoreae 3 –
Vanilleae
Galeolinae 4 4 (L), S, R Abs Stern & Judd, 1999, 2000
Vanillinae 5 4 L, S, R Abs Kohl, 1889; Solereder & Meyer, 1930; Møller &
Rasmussen, 1984; Stern & Judd, 2000
Lecanorchidinae 1 1 S, R Abs Stern & Judd, 2000
Gastrodieae
Gastrodiinae 6 2 L, S, R Abs Møller & Rasmussen, 1984; Stern, 1999
Epipogiinae 3 1 S Abs Møller & Rasmussen, 1984
Wullschlaegeliinae 1 1 S, R Abs Møller & Rasmussen, 1984; Stern, 1999
Nervilieae 1 1 L, S Abs Møller & Rasmussen, 1984
394 THE BOTANICAL REVIEW
Table II, continued
Subfamily, tribe, subtribe
No. of
genera
No.
studied
Location /
organs
studied Type Notes References
Cymbidioid phylad
Malaxideae 6 3 L, S Abs Solereder & Meyer, 1930; Møller & Rasmussen,
1984
Calypsoeae 9 3 L, S Abs Solereder & Meyer, 1930; Møller & Rasmussen,
1984
Cymbidieae
Goveniinae 1 1 L, S, R C (rough) in L Stern & Judd, 2002
Bromheadiinae 1 1 L, S C (rough) in L Møller & Rasmussen, 1984; Stern & Judd, 2002
Eulophiinae 6 5 L, S, R C (rough) in L, S Møller & Rasmussen, 1984; Stern & Judd, 2002
Thecostelinae 2 1 L, S C (rough) in L, S Møller & Rasmussen, 1984; Yukawa & Stern, 2002
Cyrtopodiinae 12 11 L, S, R C (rough) in L, S C in pericycle of R
of3Cymbidium
spp.
Solereder & Meyer, 1930; Møller & Rasmussen,
1984; Yukawa & Stern, 2002; Stern & Judd, 2002
Acriopsidinae 1 1 L, S, R C (rough) in L, S Møller & Rasmussen, 1984; Stern & Judd, 2001; Yu-
kawa & Stern, 2002
Catasetinae 5 5 L, S, R C (rough) in L, S Abs in S of 1 genus Møller & Rasmussen, 1984; Stern & Judd, 2001
Maxillarieae
Cryptarrheninae 1 –
Zygopetalinae 30 3 L, S C, ? Kohl, 1889; Hering, 1900; Solereder & Meyer, 1930
Lycastinae 8 3 C In R of a few spp.
of 5 genera
Solereder & Meyer, 1930; Holtzmeier et al., 1998;
Yukawa & Stern, 2002
Maxillariinae 8 4 L, S, (R) C (rough) C in R of 1 Maxil-
laria sp.
Solereder & Meyer, 1930; Møller & Rasmussen,
1984; Holtzmeier et al., 1998; Toscano de Brito,
1998; Davies, 1999
Stanhopeinae 22 19 L, S, R C in L, S Solereder & Meyer, 1930; Møller & Rasmussen,
1984; Stern & Morris, 1992; Stern & Whitten,
1999
Telipogoninae 4 2 L C, Abs Møller & Rasmussen, 1984; Toscano de Brito, 1998
SILICA BODIES IN MONOCOTYLEDONS 395
Ornithocephalinae 14 13 L C, Abs C in spp. of 5
genera
Møller & Rasmussen, 1984; Toscano de Brito, 1998
Oncidiinae 77 14 L, S C (irreg.) Pfitzer, 1877; Kohl, 1889; Solereder & Meyer, 1930;
Møller & Rasmussen, 1984; Toscano de Brito,
1998
Epidendroid phylad
Arethuseae
Arethusinae 2 –
Bletiinae 21 9 L, (S) C, Abs Abs. in S Solereder & Meyer, 1930; Møller & Rasmussen,
1984
Chysine 1 1 L C Solereder & Meyer, 1930
Coelogyneae
Thuniinae 1 1 L, S C Pfitzer, 1877; Møller & Rasmussen, 1984
Coelogyninae 20 6 L, S C, (Abs) Zörnig, 1903; Solereder & Meyer, 1930; Møller &
Rasmussen, 1984
Epidendreae I
Sobraliinae 4 2 L, S Abs Solereder & Meyer, 1930; Møller & Rasmussen,
1984
Arpophyllinae 1 1 L, S C Møller & Rasmussen, 1984
Meiracylliinae 1 –
Coeliinae 1 –
Laeliinae 43 7 L C Kohl, 1889; Solereder & Meyer, 1930; Møller &
Rasmussen, 1984
Pleurophallidinae 28 4 L, S C, irreg., Abs Kohl, 1889; Solereder & Meyer, 1930; Pridgeon &
Stern, 1982; Møller & Rasmussen, 1984
Epidendreae II
Glomerinae 7 3 L, S C Møller & Rasmussen, 1984
Adrorhizinae 2 1 L C Møller & Rasmussen, 1984
Polystachyinae 4 1 L, S Abs Møller & Rasmussen, 1984
396 THE BOTANICAL REVIEW
Table II, continued
Subfamily, tribe, subtribe
No. of
genera
No.
studied
Location /
organs
studied Type Notes References
Dendrobioid subclade
Podochileae
Eriinae 10 4 L, S Sph, Abs, (C) C (nodular) in
1Eria sp.
Solereder & Meyer, 1930; Møller & Rasmussen,
1984; Dressler & Cook, 1988; Yan Peng Ng
(pers. comm., 2000)
Podochilinae 6 2 L, S Sph Solereder & Meyer, 1930; Møller & Rasmussen,
1984
Thelasiinae 6 2 L, S Abs Møller & Rasmussen, 1984
Ridleyellinae 1 –
Dendrobiinae 6 6 L, S Sph (rough), Abs Abs in 6 Pseuderia
&2Dendrobium
spp.
Kohl, 1889; Solereder & Meyer, 1930; Møller &
Rasmussen, 1984; Morris et al., 1996; Carlsward
et al., 1997
Bulbophyllinae 15 6 L, S Abs
Vandeae
Aeridinae 102 14 L, (S) Sph Kohl, 1889; Dixon, 1894; Hering, 1900; Solereder &
Meyer, 1930; Møller & Rasmussen, 1984
Angraecinae 19 3 L, (S) Sph Irreg. in S Hering, 1900; Solereder & Meyer, 1930; Møller &
Rasmussen, 1984
Aerangidinae 36 4 L, S Sph Hering, 1900; Solereder & Meyer, 1930; Møller &
Rasmussen, 1984
Unplaced
Arundinae 2 1 L, S C Møller & Rasmussen, 1984
Collabiinae 3 1 L, S Abs Møller & Rasmussen, 1984
Pogoniinae 5 –
SILICA BODIES IN MONOCOTYLEDONS 397
Fig. 2. Various silica body morphologies found in Orchidaceae, Arecaceae and the order Comme-
linales. A. Cephalanthera pallens (Orchidaceae), conical silica bodies with truncated tops (hat shaped)
adjacent to phloem cells (bar = 10
m). B. Angraecum chevalieri (Orchidaceae), spherical bodies
overlying sclerenchymatous bundle-sheath cells (bar = 10
m). C. Drymophloeus beguinii (Arecaceae),
irregularly spherical bodies in vascular bundle-sheath cells (bar = 10
m). D. Cyanotis arachnoidea
(Commelinaceae), small, spherical, spinulose bodies in epidermal cells, apparently following the cell
wall (bar = 20
m). E. Conostylis bracteata (Haemodoraceae), large quantities of silica sand in vascu-
lar bundle-sheath cells (bar = 10
m). F. Anigozanthos flavida (Haemodoraceae) epidermal cells con-
taining silica sand (bar = 10
m).
stem (Judd et al., 1993; Stern et al., 1993a). Since their basal position makes apostasioids
critical in evolutionary assessments of orchid structures, this record of both types of silica body
in a single species (A. wallichii) indicates that both types originally occurred in the family and
that either both types or the spherical type alone were later lost, with a subsequent regain of the
spherical type in two epidendroid groups. However, independent origin of both types in Apostasia
is equally plausible.
398 THE BOTANICAL REVIEW
B. COMMELINIDS
The commelinids (or commelinoids) have been identified as a monophyletic clade in sev-
eral successive molecular and combined morphological/molecular analyses (e.g., Chase et al.,
1995a, 1995b, 2000; Stevenson et al., 2000). Some highly consistent non-molecular (anatomi-
cal) characters support the commelinid clade: 1) the presence of cell-wall ferulates, almost
entirely absent from non-commelinid monocotyledons (Harris & Hartley, 1980; Rudall &
Caddick, 1994); 2) the presence of silica bodies in many commelinid taxa, absent from most
non-commelinid monocotyledons except orchids; 3) the presence of Strelitzia-type surface waxes
(long, often curly, extruded wax ribbons) in some commelinids, virtually absent from non-
commelinids (Barthlott & Frölich, 1983; Frölich & Barthlott, 1988); and 4) stomatal develop-
ment by non-oblique cell division, as opposed to oblique division in most non-commelinids
(Tomlinson, 1974).
Several taxa formerly had controversial systematic placement in monocotyledons. Pan-
danaceae, Cyclanthaceae and Velloziaceae were previously considered commelinid (for ex-
ample, by Dahlgren et al., 1985), but recent molecular systematic studies (e.g., Chase et al.,
1995b, 2000) have conclusively demonstrated that they are more closely related to non-
commelinid groups. Apparent reports of silica bodies are based on confusion with crystals;
e.g., Lim and Stone (1971) for Freycinetia. They all lack silica bodies (Table I), which is
consistent with a non-commelinid placement (although, admittedly, absence of silica bodies is
non-informative for systematics in this context, since it is the plesiomorphic condition for this
character within monocotyledons). On the other hand, the presence of silica bodies in Dasypo-
gonaceae (Rudall & Chase, 1996), Hanguanaceae (Solereder & Meyer, 1929; Smithson, 1956;
Tomlinson, 1969; Tillich & Sill, 1999) and Haemodoraceae (Prychid et al., 2003) supports
their inclusion in the commelinid clade, together with other morphological and molecular data
(see below).
Although Dasypogonaceae remain unplaced among the commelinids, three other major
commelinid clades have been identified (e.g., Chase et al., 2000; Stevenson et al., 2000):
1) Arecales (Arecaceae); 2) a broadly circumscribed Poales; and 3) a “ZHC” clade consisting
of Zingiberales, Commelinales and Hanguana. However, phylogenetic relationships between
these clades remain unresolved, pending further analyses. A stable phylogeny is critical in
evolutionary assessments of characters such as presence of silica bodies. For example, if
Arecaceae are sister to other commelinids, as tentatively indicated by some analyses (e.g.,
Givnish et al., 1999; Chase et al., 2000), it would seem likely that the presence of silica bodies
is a synapomorphy for the commelinid clade and that its absence from some taxa (Table III)
represents one or more secondary reversals.
1. Arecaceae
The earliest work on silica in palms was mentioned above (see section III, “Historical Re-
view”). The first comprehensive anatomical study of palms was that of Tomlinson (1961b),
who described the types and distribution of silica bodies in all the major taxonomic groups.
Silica bodies occur in stegmata in continuous or discontinuous longitudinal files adjacent to
fibers sheathing vascular bundles or independent fiber strands. They are most frequent in leaves
and stems but are also seen next to cortical sclerenchymatous strands in roots. They do not
occur in the epidermis, but hypodermal stegmata may occasionally intrude between epidermal
cells and therefore wrongly appear to be epidermal (e.g., in Borassus: Eberwein, 1903).
There are two types of silica body and silica cell in palms, in both cases with a single silica
body per cell: 1) conical or hat-shaped bodies with a smooth base, a rough or spiny surface and
SILICA BODIES IN MONOCOTYLEDONS 399
Table III
Distribution of silica bodies in leaf of Arecaceae (classification of Uhl & Dransfield, 1987).
Key: cont. = continuous; discont. = discontinuous; Hat = hat shaped; incl. = including; occ. = occasionally;
Sph = spherical; vb(s) = vascular bundles(s). Brackets indicate rare or in few taxa.
Subfamily, tribe
No. of
genera
No.
studied Location of silica in leaf Type Notes References
Coryphoideae
Corypheae 31 20 Over fibers, vb or not
(incl. transverse vbs)
⫾Sph, spiny In cont. or discont. files,
basal wall thick; also
stem, fruit
Solla, 1884 (fruit); Pfister, 1892;
Tomlinson, 1961b; Ghose &
Johri, 1987; Killmann & Hong,
1992 (stem)
Phoeniceae 1 1 Over fibers, vb or not ⫾Sph In cont. files, basal wall
thick; also stem, root
Rosanoff, 1871 (root); Tomlinson,
1961b; Ginieis, 1964; Ghose &
Johri, 1987
Borasseae 7 6 Over fibers, vb or not
(incl. transverse vbs)
Sph, spiny (+ Hat
in Lodoicea)
In ⫾cont. files, basal
wall thick; also stem,
root
Tomlinson, 1961b; Ghose & Johri,
1987
Calamoideae
Calameae 19 13 Over fibers, vb or not
(occ. transverse vbs)
⫾Sph, spiny In cont. or discont. files,
basal wall thick; also
stem (absent from
root)
Tomlinson, 1961b; Ghose & Johri,
1987; Weiner & Liese, 1990
(stem); Weiner, 1992 (stem);
Schmitt et al., 1995
Lepidocaryeae 3 2 Over fibers, vb or not
(incl. transverse vbs
in 1 genus)
⫾Sph, spiny In discont. files (basal
wall thick in 1 ge-
nus); also stem
Tomlinson, 1961b; Killmann &
Hong, 1992 (stem)
Nypoideae 1 1 Over fibers, vb or not Hat In discont. files, basal
wall scarcely thick-
ened
Tomlinson, 1961b
Ceroxyloideae
Cyclospatheae 1 1 Over fibers, vb or not Sph, large In ⫾cont. files, basal
wall ⫾unthickened
Tomlinson, 1961b
Ceroxyleae 5 1 Over fibers, vb ⫾Sph In cont. or discont. files,
basal wall thick
Tomlinson, 1961b
Hypophorbeae 5 4 Over fibers, mainly vb Hat (+ sand in
mesophyll of
1 genus)
In cont. files, basal wall
scarcely thickened;
also stem in 1 genus
Tomlinson, 1961b; Ginieis, 1964
(perianth)
400 THE BOTANICAL REVIEW
Table III,continued
Subfamily, tribe
No. of
genera
No.
studied Location of silica in leaf Type Notes References
Arecoideae
Caryoteae 3 3 Over fibers, vb or not Hat In discont. files, basal
wall scarcely thick-
ened; also stem, root
Tomlinson, 1961b; Ghose & Johri,
1987; Killmann & Hong, 1992
(stem)
Triarteae 6 4 Over fibers, vb (not
transverse vbs)
Hat In cont. files, basal wall
scarcely thickened
Tomlinson, 1961b
Podococceae 1 0 No data
Areceae, except
2 subtribes:
86 35 Over fibers, vb or not
(not transverse vbs)
(also mesophyll in 1
genus, epidermis in 1
genus)
⫾Sph or ellipti-
cal (rarely
sand in hypo-
dermis)
In cont. or discont. files,
basal wall thick; also
stem
Tomlinson, 1961b; Ghose & Johri,
1987; Killmann & Hong, 1992
(stem)
Oraniinae 2 1 Over fibers, vb or not ⫾Hat to elliptical In discont. files, basal
wall slightly thick-
ened
Tomlinson, 1961b
Sclerosper-
matinae
2 1 Over fibers, vb or not Hat In discont. files, basal
wall ⫾unthickened
Tomlinson, 1961b
Cocoeae, except
1 subtribe:
22 8 Over fibers, vb or not
(incl. transverse vbs)
⫾Sph (+ sand in
1 genus in hy-
podermis)
Most in discont. files, ba-
sal wall thick; also
stem, root, fruit
Rosanoff, 1871 (root); Molisch, 1913
(fruit); Tomlinson, 1961b; Ghose
& Johri, 1987; Killmann & Hong,
1992 (stem)
Bactridinae 6 5 Over fibers, vb or not (&
over sclereids in 1
genus)
Hat In cont. or discont. files,
basal wall scarcely
thickened; also stem,
root
Tomlinson, 1961b
Geonomeae 6 5 Over fibers, vb or not ⫾Sph (rarely el-
liptical)
In cont. or discont. files,
basal wall mostly
thick
Tomlinson, 1961b
Phytelephantoideae 3 1 Over fibers, vb or not Sph In cont. files, basal wall
thick; also stem, fruit
Molisch, 1913 (fruit); Tomlinson,
1961b
SILICA BODIES IN MONOCOTYLEDONS 401
a basal cell wall that is only slightly thickened and not conspicuously pitted; and 2) spherical
bodies, usually rather irregular, sometimes more or less ellipsoidal, also with a rough or spiny
surface (Fig. 2C), with a basal cell wall that is thickened, often pitted, and sometimes lignified
or suberized and with other walls that are thin. The development of the spherical type has been
studied by Schmitt et al. (1995) in Calamus auxillaris. These two types have not been found to
occur together except in Lodoicea, where most bodies are spherical but where large, hat-shaped
ones up to 23
m in diameter are present adjacent to transverse veins in the lamina (Tomlinson,
1961b). Raphide crystals are also common in all parts of palms.
Tomlinson (1961b) noted that conical or hat-shaped silica bodies are present in the informal
groups, which he designated as “bactroid,” “caryotoid,” “chamaedoroid,” “iriartoid” and
“nypoid” palms, while spherical bodies occur in the arecoid, borassoid, cocoid, lepidocaryoid,
phoenicoid, phytelephantoid and sabaloid palms and in some isolated genera. In Table III his
data have been rearranged according to the classification of Uhl and Dransfield (1987). Each
subtribe usually possesses only one type of silica body, apart from Lodoicea of Borasseae.
Subfamilies Coryphoideae, Calamoideae and Phytelephantoideae all have spherical silica bod-
ies, and Nypoideae have hat-shaped silica bodies. Ceroxyloideae comprise two tribes with
spherical and one with hat-shaped bodies, while Arecoideae have some tribes or subtribes with
spherical and others with hat-shaped bodies.
2. ZHC Clade (Zingiberales, Commelinales, and Hanguana)
This clade is polymorphic for presence or absence of silica bodies. In the taxonomically
isolated genus Hanguana (Hanguanaceae), silica bodies are present as irregular granular de-
posits, mainly in or near the foliar bundle-sheath cells rather than the epidermis (Solereder &
Meyer, 1929; Smithson, 1956; Tomlinson, 1969; Rudall et al., 1999; Tillich & Sill, 1999).
Hanguana belongs in a clade together with the orders Zingiberales and Commelinales, but its
precise relationships within this clade remain disputed. Morphological data indicate an affinity
with Zingiberales (e.g., Rudall et al., 1999), whereas most recent analyses of molecular data
place it within Commelinales (e.g., Chase et al., 2000; APG II, 2003).
Apart from Hanguana, there are four families in the order Commelinales: Haemodoraceae,
Commelinaceae, Philydraceae and Pontederiaceae (Table IV). Silica bodies are absent from
Philydraceae and Pontederiaceae and present in only some genera of Commelinaceae and
Haemodoraceae. Evans et al. (2000) did not include presence or absence of silica bodies in
their morphological cladistic analysis of Commelinaceae. In Commelinaceae, silica bodies had
been thought to be restricted to the tribe Tradescantieae of the subfamily Commelinoideae
(Tomlinson, 1969), where they represented a relatively consistent potential synapomorphy for
this group, although silica bodies are absent from some genera that were embedded within
Tradescantieae in the morphological analysis, such as Murdannia (Faden & Inman, 1996).
However, Faden (pers. comm., 2003) has also observed silica bodies in Dictyospermum, a
genus of the tribe Commelineae, which appear as large, silica infillings of the cell. These bod-
ies differ greatly from the epidermal (several per cell) small, spherical spinulose bodies of the
Tradescantieae that are often embedded in the outer cell wall (Fig. 2D). One exception to these
spherical bodies is a possible observation of epidermal silica sand in Zebrina pendula. This
mirrors observations in Haemodoraceae, where the silica almost always takes the form of silica
sand, the only exception to this being rare sightings of spherical bodies, possibly formed by
sand coalescence, in two genera that also possess sand. Presence of silica sand is restricted to
the subfamily Conostylidoideae (Prychid et al., 2003) and is mainly located in the vascular
bundle-sheath cells (Fig. 2E), resembling the case in Hanguana. Only one genus (Anigozanthos)
has exclusively epidermal silica sand (Fig. 2F).
(Text continues on p. 406)
402 THE BOTANICAL REVIEW
Table IV
Distribution of silica bodies in Hanguana and Commelinales (tribes based on classification of Kubitzki, 1998).
“Basal wall thickened” refers to the wall adjacent to sclerenchyma.
Silica presence/location Type & no. per cell Notes References
Hanguana (1 genus; 5+ spp.; silica seen in 1 sp.) 1) Endodermoid sheath
cells; 2) Hypodermis,
occasionally in meso-
phyll1)
1) Small, irregular,
granular; several per
cell; 2) Large bodies
Cells with U-shaped
thickenings; not seen
in root
Solereder & Meyer,
1929; Tomlinson,
1969; Tillich &
Sill, 1999
Commelinaceae (2 subfamilies, 4 tribes, 41 genera,
650 spp.)
Cartonemoideae (2)
Cartonemateae
Cartonema (6 spp., 2 examined) Absent Tomlinson, 1969
Triceratelleae
Triceratella (1 sp., 1 examined) Absent Tomlinson, 1969
Commelinoideae
Tradescantieae (several genera not examined)
Subtribe Palisotinae
Palisota (18 spp., 4 examined) Absent Tomlinson, 1969
Subtribe Cyanotinae
Belosynapsis (4 spp., 2 examined) Absent Tomlinson, 1969
Cyanotis (50 spp., 1 examined) Epidermis, intercostal Small, spherical, spinu-
lose, up to 10 µm,
few to many per cell
Not seen by Tomlinson,
1969
Prychid, pers. obs.
Subtribe Coleotrypinae
Amischotolype (Forrestia) (20 spp.,
1 examined)
Epidermis, costal & in-
tercostal
Small, spherical, spinu-
lose, up to 10 µm,
few to many per cell
Inner walls thickened;
also in stem
Möbius, 1908a; Tom-
linson, 1966,
1969; Stant, 1973
Coleotrype (9 spp., 1 examined) Epidermis, costal, rarely
intercostal
Small, spherical, spinu-
lose
Also in stem & leaf
sheath
Möbius, 1908a; Tom-
linson, 1966,
1969; Stant, 1973
SILICA BODIES IN MONOCOTYLEDONS 403
Subtribe Dichorisandrinae
Cochliostema (2 spp., 2 examined) Absent Tomlinson, 1969
Dichorisandra (25 spp., 2 examined) Absent Tomlinson, 1969
Geogenanthus (5 spp., 1 examined) Absent Tomlinson, 1969
Siderasis (2/3 spp., 1 examined) Absent Tomlinson, 1969
Subtribe Thyrsantheminae
Tinantia (13 spp., 1 examined) Absent Tomlinson, 1969
Subtribe Tradescantiinae
Callisia (incl. Hadronemas) (20 spp.,
7 examined)
Epidermis, costal 1) Small, spherical,
spinulose, up to 10
µm, few to many per
cell; 2) Tiny, 1–2 µm,
many in outer cell
wall
Also in stem & leaf
sheath
Möbius, 1908b; Tom-
linson, 1966,
1969; Stant, 1973;
Prychid, pers. obs.
Gibasis (17 spp., 6 examined) Epidermis, costal, and in-
tercostal
Small, spherical, spinu-
lose, 3–8 µm, few to
many per cell; also
on outer wall
Also in stem; no bodies
seen in G.oaxacana
Tradescantia (incl. Campelia and
Zebrina) (ca. 70 spp., 17
examined)
Present in some species;
epidermis, costal,
rarely intercostal
1) Small, sperical, spinu-
lose; 2) Silica sand
seen in Zebrina, al-
though not by Tom-
linson, 1969
Seen by Molisch, in
Campelia, not by
Tomlinson, 1969
Molisch, 1918; Tom-
linson, 1966,
1969; Prychid,
pers. obs.
Tripogandra (21 spp., 3 examined) Epidermis, costal 1) Small, spherical
spinulose; 2) Tiny,
1–2 µm, many in
outer cell wall
Also in stem Tomlinson, 1966,
1969
Commelineae (several genera not examined)
Aneilema (64 spp., 8 examined) Absent Tomlinson, 1969
Anthericopsis (1 sp., 1 examined in
Tomlinson)
Absent Faden & Inman,
1996; Evans et al.,
2000
Commelina (170 spp., 10 examined) Absent Tomlinson, 1969
404 THE BOTANICAL REVIEW
Table IV, continued
Silica presence/location Type & no. per cell Notes References
Commelinaceae, continued
Commelinoideae, continued
Commelineae, continued
Dictyospermum (5 spp., 1 examined) Faden, pers.com.
Floscopa (20 spp., 2 examined) Absent Tomlinson, 1969
Murdannia (50 spp., 5 examined) Absent Tomlinson, 1969
Pollia (17 spp., 5 examined) Absent Tomlinson, 1969
Polyspatha (3 spp., 2 examined) Absent Tomlinson, 1969
Stanfieldiella (4 spp., 1 examined) Absent Tomlinson, 1969
Haemodoraceae (2 subfamilies, 14 genera, ca. 81
spp.)
Conostylidoideae
Anigozanthos (ca. 10 spp., 7 exam-
ined)
Epidermis Sand Sand more numerous in
epidermal cells of
bifacial leaf sheath;
none seen in A. hu-
milis
Prychid et al., 2003
Blancoa (1 sp., 1 examined) 1) Bundle-sheath cells in
leaf blade; 2) Adaxial
epidermal cells of
leaf sheath
Sand
Conostylis (ca. 25 spp., 14 examined) 1) Bundle sheath cells;
2) Palisade meso-
phyll cells, in some
spp.; 3) Spongy pa-
renchyma cells, in
some spp.; 4) Rarely,
unlignified adaxial
epidermal cells of
leaf sheaths
Sand Occasionally, in C. Bea-
liana, vascular
bundle-sheath sand
appears to form a
spherical body
SILICA BODIES IN MONOCOTYLEDONS 405
Macropidia (1 sp., 1 examined) Bundle-sheath cells Small amounts of sand
Phlebocarya (3 spp., 3 examined) 1) Bundle sheath cells; 2)
Epidermal cells
Sand Small amounts occur in
central mesophyll
cells or subepidermal
layers of some spe-
cies; occasionally
vascular bundle
sheath sand coalesces
into a spherical body,
in some species
Tribonanthes (5 spp., 1 examined) Bundle-sheath cells Small amounts of sand
Haemodoroideae (several genera not examined)
Dilatris (5 spp., 3 examined) Absent
Haemodorum (20 spp., 6 examined) Absent
Lacnanthes (1 sp., 1 examined) Absent
Wachendorfia (5 spp., 2 examined) Absent
Philydraceae (4 genera, 5 spp.)
Helmholtzia, Orthothylax, Philydrum,
Phildrella (all species examined)
Absent Rowlatt, unpublished
Pontederiaceae (9 genera, 33 spp.)
5 genera, ca. 20 spp. examined Absent Rowlatt, unpublished
406 THE BOTANICAL REVIEW
Within the order Zingiberales, silica bodies are present in all families (Table V) (Tomlinson,
1969), mostly restricted to the vascular bundle-sheath cells (in Cannaceae (Fig. 3A), Costaceae
(Fig. 3B), Heliconiaceae (Figs. 3C, 3D), Lowiaceae (Fig. 3E), Marantaceae (Figs. 3F, 3G),
Musaceae (Figs. 3H, 4A, 4B), and some genera of Strelitziaceae (Figs. 4C, 4D), often in a
hypodermal region adjacent to bundle-sheath sclerenchyma. There are occasional records of
silica bodies in other mesophyll cells (Heliconiaceae, Marantaceae, Zingiberaceae), and they
are also present in the epidermis in Phenakospermum (Strelitziaceae) and most Zingiberaceae
(Figs. 4F, 4G) (Tomlinson, 1969). Silica bodies in Zingiberales are druse-like (i.e., spherical
with a rugose surface) in most genera, but with some exceptions: they are more or less conical
in Orchidantha (Lowiaceae) (Fig. 3E) and some Marantaceae, “trough shaped” (i.e., rectangu-
lar with a central shallow depression) in most Heliconiaceae and Musaceae and present as
epidermal silica sand in some Zingiberaceae, rarely in Marantaceae, Strelitziaceae and Musaceae
(Fig. 3H). Kress et al. (2001) discussed evolutionary relationships of Zingiberales families
using molecular and morphological data. They concluded that Zingiberales are monophyletic,
with three sets of sister families: Strelitziaceae + Lowiaceae, Costaceae + Zingiberaceae and
Cannanceae + Marantaceae. Of these, Costaceae and Marantaceae have broadly similar silica
body types and locations, Lowiaceae and Strelitziaceae have bodies in similar locations but
different shapes, Costaceae and Zingiberaceae differ in that Costaceae has bodies over scleren-
chymatous bundle sheaths, while Zingiberaceae have predominantly sand or small bodies in
epidermal cells.
3. Poales
A broad circumscription of the order Poales is now widely adopted (e.g., APG, 1998; Chase
et al., 2000; APG II, 2003). There are two well-defined major clades, the sedge clade (Cyperaceae,
Juncaceae, Thurniaceae and Prioniaceae) and the grass clade (Poaceae, Restionaceae and their
allies), plus several other families (Bromeliaceae, Hydatellaceae, Mayacaceae, Rapateaceae,
Sparganiaceae, Typhaceae and Xyridaceae) whose relationships remain unresolved. Silica bodies
are absent from several families of Poales (Table VI), and this may represent a synapomorphy
for some groups. In particular, the absence of silica bodies in Hydatellaceae may support a
putative relationship between them and Xyridaceae, Eriocaulaceae and Mayacaceae
(Michelangeli et al., 2003), all of which lack silica bodies. In contrast to many other commelinids
(especially Zingiberales and palms), in most Poales that possess silica bodies they are restricted
to the epidermis, with the exception of some species of Bromeliaceae, Ecdeiocoleaceae,
Flagellariaceae, Joinvilleaceae, Juncaceae, Restionaceae (Table VII) and Thurniaceae, in which
they occur in other tissues, especially the vascular bundle sheath. In Rapateaceae, all genera
possess characteristic spherical silica bodies in the epidermis (Table VIII) (Carlquist, 1966;
Carlquist in Tomlinson, 1969), rather similar to those of Commelinaceae-Tradescantieae, al-
though this must be regarded as a homoplasy, since the two groups belong in different clades
within the commelinids.
In the sedge clade, silica bodies are common in most groups of Cyperaceae (Table IX), in
which they possess a conical form, often with small spines (satellites) around the base (Figs.
5A, 5B), but rare or absent in some genera of the sedge tribe Hypolytreae, which is the putative
sister group to the rest of the family (Muasya et al., 1998, 2000). The distribution and types of
silica bodies in leaves of Cyperaceae have been described by Metcalfe (1971), who summa-
rized early work on the family; subsequent research has extended the observations but not
altered the main conclusions. The most characteristic type of silica body is conical, with the
base resting on the usually thickened, inner periclinal wall of an epidermal cell (rarely on
anticlinal or outer periclinal walls). There may be one to numerous bodies per cell on a single
(Text continues on p. 422)
SILICA BODIES IN MONOCOTYLEDONS 407
Table V
Distribution of silica bodies in Zingiberales (classification from Kubitzki, 1998).
Key: LS = longitudinal section; par = parenchyma; scl = sclerenchyma; vb(s) = vascular bundle(s).
Basal wall refers to wall adjacent to sclerenchyma.
Silica presence / location in leaf Type & no. per cell Notes References
Cannaceae (1genus, 10–25 spp.)
Canna (4 spp. examined) Over vb scl sheath; hypodermis Druse-like, 1 per cell, in
thin-walled cells, in files
in LS
In petiole, stem, rhizome,
not root
Tomlinson, 1961a,
1969
Costaceae (4 genera, 100 spp.)
Costus (3 spp. examined);
Tapeinochilus (1 sp. exam-
ined)
Over vb scl sheath Druse-like to irregularly
spiny, 1 per cell; cells
often forming complete
layer around vbs
In petiole, stem, rhizome,
not root
Tomlinson, 1956,
1962, 1969
Heliconiaceae (1 genus, 200 spp.)
Heliconia (14 spp. examined) 1) Over vb sheath fibers & over par
sheath; 2) Palisade of 1 sp.
1) Trough shaped; spines
projecting from base into
pits in wall; 1 per cell; 2)
irregularly spherical, 1
per cell
Basal wall thickened; cells
in files in LS. Also in
stem & rhizome, not in
root
Tomlinson, 1959,
1969; Prychid,
pers. obs.
Lowiaceae (1 genus, 10 spp.)
Orchidantha (3–4 spp. exam-
ined)
Over vb fibers ⫾Conical; top may be trun-
cated, 1 per cell; small
fingers of silica may
project from the base of
the body into the cell
wall
Basal wall thickened; cells
in files in LS; also in
petiole, rhizome, not root
Tomlinson, 1959,
1969
408 THE BOTANICAL REVIEW
Table V, continued
Silica presence / location in leaf Type & no. per cell Notes References
Marantaceae (31 genera, 550 spp.; no currently accepted subfamilies or tribes)
17 genera, 37 spp. examined 1) Over vb scl sheath (rarely hypo-
dermis); 2) Over scl of trans-
verse vbs; 3) Mesophyll, below
palisade
1) Hat shaped, base flat;
nodular or spiny, up to
20 mm, 1 per cell; 2) As
in 1), but smaller, 1 per
cell; 3) Druse-like, up to
35 µm, 1 per cell
1) Basal wall thickened;
cells in files in LS;
2) Basal wall thickened;
cells in files (rarely clus-
ters) in LS; 1) & 2) Also
in stem, not root; 3) In
large, thin-walled
cells.Some bodies appear
very irregular in Thalia
geniculata.T. welwitchii
and Sarcophrynium mac-
rostachyum have possi-
ble sand (Prychid, pers.
obs.)
Petersen, 1893; Tom-
linson, 1961b,
1969
Calathea, Ctenanthe, Ischnosi-
phon, Maranta, Mono-
tagma, Stromanthe, etc.
Mesophyll, usually in palisade Druse-like, or elongated,
most small, 3–5 µm (up
to 20 µminCtenanthe)
Possible sand in Maranta
oligantha (Prychid, pers.
obs.)
Tomlinson, 1961b,
1969
Donax, Saranthe Sand
Musaceae (2 genera, 40 spp.)
Ensete (4 spp. examined);
Musa (ca. 25 spp. exam-
ined)
1) Over vb sheath fibers; 2) In pa-
renchymatous sheath of trans-
verse vbs & occasionally in
transverse septa
1) Rectangular in surface
view, with central shal-
low depression (trough
shaped) ; spines project-
ing from base into pits in
wall, 1 per cell; 2) Ir-
regularly spherical, 1 per
cell
In files in LS; also in stem
and seed, not root; epi-
dermal silica sand also
seen in M.schizocarpa
and M. sapientum
Tomlinson, 1959,
1969; Graven et
al.; Prychid, pers.
obs.
SILICA BODIES IN MONOCOTYLEDONS 409
Strelitziaceae (3 genera, 6 spp.)
Phenakospermum (1 sp. exam-
ined)
1) Over vb sheath fibers & girders;
also in transverse septa; 2) Epi-
dermis over scl
1) & 2) Spherical, spiny, in
thin-walled cells, 1 per
cell; 1) Sand may also be
present
In files in LS; also in stem,
not in root
Tomlinson, 1959,
1960, 1969
Ravenala (1 sp. examined) 1) Over vb sheath fibers & girders;
also in transverse septa; 2) Epi-
dermis over scl
1) & 2) Spherical, spiny, in
thin-walled cells, 1 per
cell; 1) Sand may also be
present
Strelitzia (4–5 spp. examined) 1) Over vb sheath fibers & girders;
also in transverse septa; 2) Epi-
dermis over scl
1) & 2) Spherical, spiny, in
thin-walled cells, 1 per
cell; 1) Sand may also be
present
Zingiberaceae (50 genera, ca. 1300 spp.)
Alpinieae (21 genera, ca. 700
spp.) (8 genera, 15 spp.
examined)
Epidermis over scl (internal in
Hornstedtia conica only)
1) Small, irregularly spheri-
cal, 1 per cell; 2) Sand
Sand in other organs, not in
root; spherical, warty in
Elettaria seed
Tomlinson, 1956,
1962, 1969; Webb
& Arnott, 1982
Hedychieae (19 genera, ca. 300
spp.) (9 genera, 23 spp.
examined)
Epidermis (rarely mesophyll, vb
sheath) (internal in Kaempferia
only)
Sand; Kaempferia: small, ir-
regularly spherical, 1 per
cell
Small, irregularly spherical
costal and rarely inter-
costal bodies observed in
G.leucantha (Prychid,
pers. obs.)
Zingibereae (1 genus, ca. 100
spp.) (Zingiber: 2 spp.
examined)
Epidermis over scl 1) Small, irregularly spheri-
cal, 1 per cell; 2) Sand
410 THE BOTANICAL REVIEW
Fig. 3. Various silica body morphologies found in the order Zingiberales. A. Canna edulis (Cannaceae),
druse-like silica bodies over vascular bundle sheath (bar = 10
m). B. Costus englerianus (Costaceae), druse-
like silica bodies over bundle-sheath cells (bar = 20
m). C. Heliconia psittacorum (Heliconiaceae), trough-
shaped silica bodies over vascular bundle-sheath fibers (bar = 20
m). D. Heliconia aff. tortuosa
(Heliconiaceae), trough-shaped silica bodies with silica fingers projecting from the base into the cell wall (bar
= 10
m). E. Orchidantha sp. (Lowiaceae), truncated conical silica bodies overlying a vascular bundle (bar =
10
m). F. Maranta arundinacea (Marantaceae), costal silica bodies in mesophyll cells (bar = 10
m).
G. Marantochloa purpurea (Marantaceae), a druse-like intercostal silica body in a mesophyll cell (bar = 20
m). H. Musa schizocarpa (Musaceae), intercostal, epidermal silica sand (bar = 10
m).
SILICA BODIES IN MONOCOTYLEDONS 411
Fig. 4. Various silica body morphologies found in the order Zingiberales, continued. A. Musa coccinea
(Musaceae), trough-shaped silica bodies overlying a vascular bundle (bar = 10
m). B. Musa sp. (Musaceae),
trough-shaped silica bodies with silica fingers projecting from the base into cell-wall pits (bar = 10
m).
C. Ravenala madagascariensis (Strelitziaceae), spiny silica bodies in vascular bundle-sheath cells (bar =
10
m). D. Strelitzia augusta (Strelitziaceae), a bundle-sheath cell containing a druse-like silica body (bar
= 20
m). E. Kaempferia aethiopia (Zingiberaceae), an internal costal silica body (bar = 10
m).
F. Hornstedtia conica (Zingiberaceae), epidermal, intercostal silica sand (bar = 10
m). G. Alpinia
conchigera Zingiberaceae), two forms of silica: intercostal silica sand and costal spherical bodies in
epidermal cells (bar = 10
m).
412 THE BOTANICAL REVIEW
Table VI
Distribution of silica bodies in Poales.
Key: LS = longitudinal section; scl = sclerenchyma; vb = vascular bundle.
Silica presence / location Type & no. of silica bodies per cell Notes References
Anarthriaceae (1 genus, 7 spp.)
Anarthria (5 spp. examined) Absent Cutler, 1969
Bromeliaceae (56 genera, 2600+ spp.)
Most genera (37 genera,
106 spp. examined) Epidermis, intercostal &
costal
Spherical, spinulose, up to 10 µm,
1 per cell; bodies larger over scl,
may be absent from cells over
thin-walled hypodermis
Outer wall thin, inner wall
thickened; never in sto-
mata; also present in
stem
Tomlinson, 1969;
see also
Bulitsch,
1892b; Lins-
bauer, 1911
Cryptanthus (1 sp. examined) Epidermis, intercostal &
costal
Spherical, spinulose, aggregates of
several per cell
Tomlinson, 1969
Tillandsia (20 spp. examined) Epidermis, intercostal Silica sand Present in hypodermis in
T. andicola (Baumert,
1907); spherical, spinu-
lose bodies seen in
T. stricta and possible
bodies in T. usneoides
(Prychid pers. obs.)
Baumert, 1907;
Tomlinson,
1969
8 genera (some spp.) Outer bundle sheath Silica sand Tomlinson, 1969
Centrolepidaceae (3 genera, 35 spp.)
Aphelia (5 spp., 5 examined) (Epidermis) (Irregular, in 1 sp.) Silica-like? Not seen in culm Cutler, 1969
Centrolepis (c. 28 spp., 10
examined)
(Epidermis, ground tissue) (Particles or sand in 2 spp.) Silica? Also in culm of
3 spp.
Gaimardia (3 spp., 3 exam-
ined)
(Epidermis) (Rectangular, in 1 sp.) Silica?
Cyperaceae (104 genera, 5000+ spp.)
Most genera & 86 spp. exam-
ined
Epidermis, costal (rarely in-
tercostal)
Conical ⫾satellites (rarely nodular,
bridges, other types)
See Table VIII for details Metcalfe, 1971
SILICA BODIES IN MONOCOTYLEDONS 413
Ecdeiocoleaceae (2 genera, 2 spp.)
Ecdeiocolea (1 sp., 1 exam-
ined)
Chlorenchyma (culm); epi-
dermis, costal (culm)
Sand (culm) None seen in leaf Cutler, 1969;
Prychid, pers.
obs.
Eriocaulaceae (10 genera, 700–1400 spp.)
9 genera (6 examined) Absent N/A Tomlinson, 1965,
1969
Flagellariaceae (1 genus, 4 spp.)
Flagellaria (1 sp. examined) Above & below vb fibrous
sheaths
Small, irregular, in small cells;
1 per cell
Never epidermal; cells usu-
ally in longitudinal files
Tomlinson, 1969
Hydatellaceae (2 genera, 10 spp.)
Hydatella (2 spp., 1 examined) Absent N/A Cutler, 1969
Trithuria (3 spp., 2 examined) Absent N/A
Joinvilleaceae (1 genus, 2 spp.)
Joinvillea (2 spp. examined) 1) Epidermis, short cells;
2) Vb fiber sheath
1) Smooth cubical bodies,
1 per cell, filling lumen;
2) Irregular nodular bodies,
1 per cell; cells in files in LS
Short cells alternating with
long cells in epidermis;
silicification of meso-
phyll cells
Tomlinson, 1969
Juncaceae (8 genera, 350 spp.)
Prionium, Marsippospermum,
Rostkovia, Distichia, Pato-
sia, Oxychloe, Luzula
Absent Cutler, 1969
Juncus 1) Vb fiber sheath; 2) Rarely
mesophyll
Sand Prychid pers. obs.
Mayacaceae (1 genus, 4–10 spp.)
Mayaca (4/3) Absent N/A Tomlinson, 1969
Poaceae (700+ genera, 10,000+ spp.)
Epidermis Many shapes, not usually conical or
spherical
Absent from some genera &
spp; distribution will be
discussed in another pub-
lication
Metcalfe, 1960
414 THE BOTANICAL REVIEW
Table VI,continued
Silica presence / location Type & no. of silica bodies per cell Notes References
Prioniaceae (1 genus)
Prionium Absent N/A Cutler, 1969
Rapateaceae (16 genera; 80 spp.)
Epidermis Spherical; see Table VIII for details See Table IX for details Carlquist, 1966;
Carlquist, in
Tomlinson,
1969
Restionaceae (55 genera; 490 spp.)
1) Bundle sheaths; 2) Paren-
chyma sheath, ground
tissue
1) Spherical-nodular; 2) Irregular or
granular
Silica present in culms
(most genera leafless);
see Table VII for
details
Cutler, 1969
Thurniaceae (1 genus; 3 spp.)
Thurnia (2 spp. examined) Epidermis (1 sp.); Paren-
chyma
(1 sp.)
Nodular, several per cell, over scl;
sand
Also present in culm Cutler, 1969
Typhaceae (2 genera; 16–30 spp.)
Sparganium (14 spp.,
10 examined)
Absent N/A Solereder &
Meyer, 1933;
Kaul, 1972;
Rowlatt, un-
published
Typha (8–13 spp., 8 examined) Absent N/A Meyer, 1933; Row-
latt, unpub-
lished
Xyridaceae (5 genera; 300 spp.)
Abolboda, Achlyphila, Aratity-
opea, Orectanthe, Xyris
Absent N/A Tomlinson, 1969
SILICA BODIES IN MONOCOTYLEDONS 415
Table VII
Distribution of silica bodies in culm of Restionaceae (classification of Linder et al., 1998).
Key: Abs = absent; chlor = chlorenchyma; epid = epidermis; par = parenchyma; scl = sclerenchyma; Sph = spherical-nodular.
Brackets indicate rarely present or present in a few taxa.
Genera for which no data are available have been omitted from the table.
Genus No. of species No. studied Distribution Type and location in culm Notes References
Hopkinsia 2 1 Australia Abs Cutler, 1969
Lyginia 3 1 or 2 Australia Abs Crystals present in this
genus only
Solereder & Meyer, 1929;
Cutler, 1969
Staberoha ca. 9 5 South Africa Abs Solereder & Meyer, 1929;
Cutler, 1969
Ischyrolepis ca. 48 1+? South Africa ⫾Sph in par sheath
& ground tissue
Cutler, 1969
Elegia ca. 35 21 South Africa Abs Cutler, 1969
Chondropetalum,
Dovea, Askido-
sperma
ca. 24 16 South Africa Abs Cutler, 1969
Platycaulos,Restio ca. 100 ca. 60 South Africa,
Zaire, Mada-
gascar
Sph in par sheath (&
chlor); granular in
par sheath &/or
ground tissue, protec-
tive cells, chlor; Abs
in many spp.
Restio groups 3–6 in Cut-
ler; all his Australian
spp. now in other
genera
Solereder & Meyer, 1929;
Cutler, 1969
Calopsis ca. 23 8 South Africa Abs in 5 spp.; Sph in par
sheath or chlor
(2 spp.); irregular in
protective cells (1 sp.)
South African Leptocar-
pus spp. in Cutler
Cutler, 1969
Thamnochortus ca. 34 20 South Africa Abs (irregular in epid in
T. bachmannii only)
Granular bodies in T. flori-
bundus; rough, Sph
body in T. insignis.
Possible sand in
T. scabridus (Prychid,
pers. obs.)
Solereder & Meyer, 1929;
Cutler, 1969
416 THE BOTANICAL REVIEW
Table VII, continued
Genus No. of species No. studied Distribution Type and location in culm Notes References
Rhodocoma 7 2 South Africa Abs Cutler, 1969
Ceratocarya ca. 6 1? South Africa Sph in par sheath Cutler, 1969
Cannomois ca. 7 6 South Africa Sph in par sheath & scl
ribs
Cutler, 1969
Anthochortus ca. 15 2+? South Africa Sph in par sheath Incl. Phyllocomos &
Hypolaena p. p.
Cutler, 1969
Mastersiella 3 3? South Africa Sph in scl sheath; granular
in ground tissue or
Abs
Incl. Hypolaena p. p. Cutler, 1969
Hypodiscus ca. 15 ca. 9 South Africa Sph in scl sheath or Abs Solereder & Meyer, 1929;
Cutler, 1969
Willdenowia ca. 12 7 South Africa Sph in par sheath or scl
sheath; granular in
ground tissue
Solereder & Meyer, 1929;
Cutler, 1969
Lepyrodia 22 ca. 9 Australia Sph, 1 per cell in epid;
granular in ground tis-
sue (some spp.) & par
sheath (1 sp.)
Lepyrodia group 2 in
Cutler
Solereder & Meyer, 1929;
Cutler, 1969
Sporadanthus 7 5 Australia, New
Zealand
granular in epid (2 spp.);
Abs (3 spp.)
Lepyrodia group 1 & Spo-
radanthus in Cutler
Cutler, 1969
Calorophus 2 1 Australia Abs See also Empodisma Cutler, 1969
Empodisma 2 2 Australia, New
Zealand
Sph in par sheath; granu-
lar in ground tissue
2 spp. separated from
Calorophus
Cutler, 1969; Johnson &
Cutler, 1973
Coleocarya 1 1 Australia Sph in par sheath Cutler, 1969
Desmocladus 16 ? Australia Incl. in Hypolaena in Cut-
ler
Cutler, 1969
Harperia 4 1 Australia Sph in scl sheath; irregu-
lar & granular in epid
& ground tissue
Cutler, 1969
Onychosepalum 3 1 Australia Sph in par sheath, 1 per
cell
Cutler, 1969
SILICA BODIES IN MONOCOTYLEDONS 417
Lepidobolus 8 3 Australia Sph in par sheath &
ground tissue; granular
in ground tissue
Solereder & Meyer, 1929;
Cutler, 1969
Australian genera
separated from
Restio
ca. 36 24 Australia Sph in par sheath or scl
sheath in most spp.;
(granular in ground
tissue in few spp.)
Restio groups 1, 2, 7–10
in Cutler
Cutler, 1969
Dielsia 1 1 Australia Sph in par sheath Sand in layer of cells im-
mediately adjacent to
central space, also in
bundle sheath (Pry-
chid, pers. obs.)
Cutler, 1969
Loxocarya 5 5? Australia Sph in par sheath or scl
sheath
Solereder & Meyer, 1929;
Cutler, 1969
Leptocarpus, Mee-
boldina
13 ca. 8 Australia Sph in par sheath or scl
sheath; irregular or
granular in pillar cells,
chlor, ground tissue
African Leptocarpus spp.
now in Calopsis
Solereder & Meyer, 1929;
Cutler, 1969
Hypolaena 8 3 Australia Sph in scl sheath Hypolaena group 2 in
Cutler (Australian
spp.)
Solereder & Meyer, 1929;
Cutler, 1969
Chaetanthus 3 1 Australia Sph in par sheath; granu-
lar in pillar cells
Cutler, 1969
Dapsilanthus 4 1? Australia, South-
east Asia,
New Guinea
Sph in scl sheath Separated from Leptocar-
pus; as L. disjunctus in
Cutler
Cutler, 1969
Apodasmia 4 2? Australia, New
Zealand,
Chile
Sph in scl sheath; granular
in chlor, ground tissue,
hairs
Separated from Leptocar-
pus; as L. chilensis &
L. simplex in Cutler
Cutler, 1969
418 THE BOTANICAL REVIEW
Table VIII
Distribution of silica bodies in Rapateaceae (14 genera; 80 spp.)
(data from Carlquist, 1966; Carlquist, in Tomlinson, 1969; Prychid, pers. obs.)
Type and location Notes
Saxofridericioideae
Saxofridericieae: Epidryos (1 sp. examined),
Phelpsiella (1 sp. examined), Saxofridericia
(2 spp. examined), Stegolepis (2 spp. exam-
ined), Amphiphyllum (1 sp. examined),
Marahuacea not examined
Present in leaf epidermis; small, spherical, rough or
spiny; several per cell
Silica absent from stem
Rapateoideae
Rapateae: Rapatea (7 spp. examined), Cephalo-
stemon (1 sp. examined), Duckea (3 spp.
examined), Spathanthus (2 spp. examined)
Present in leaf epidermis, sometimes over fibers in
Rapatea; in Rapatea, Cephalostemon and Duckea
spherical, rough or spiny, several to many per cell;
in Spathanthus large, rough, 1 per cell or aggre-
gates of sand
Silica sand and or small silica bodies in
stem in Spathanthus and Monotremeae
Monotremeae: Monotrema (4 spp. examined),
Maschalocephalus (1 sp. examined), Potaro-
phytum (1 sp. examined), Windsorina not
examined
Present in leaf epidermis; spherical, rough or spiny,
several to many per cell, and/or silica sand
SILICA BODIES IN MONOCOTYLEDONS 419
Table IX
Distribution of silica bodies in leaf of Cyperaceae (classification of Goetghebeur, 1998).
Key to location: Abs = absent; epc = epidermis, costal regions; epic = epidermis, intercostal regions;
par = parenchyma; subep = subepidermis; vb = vascular bundle.
Key to type: Br = bridge; C = conical; C+sat = conical with satellites; Nod = nodular; Pyr = pyriform; Si = silica; Sph = spherical.
Brackets indicate occasionally present or present in a few taxa.
Subfamily, tribe
No. of
genera
No.
studied
Type of silica, no. of bodies
per cell and location in leaf Notes References
Mapanioideae
Hypolytreae 9 8 Abs or C, Br, wedges
(warty), 1–3(–11) per
cell, in epc/epic (subep)
In sinuations of anticlinal
walls (rarely in lumina)
Pfeiffer, 1921b, 1925, 1927; Duval-Jouve, 1873a,
1873b; Koyama, 1966; Metcalfe, 1971
Chrysitricheae 4 3 Abs or C (C+sat) in epc Walls may be silicified Pfeiffer, 1920a, 1921a, 1927; Metcalfe, 1971
Cyperoideae
Scirpeae 6 3 C (C+sat), (Nod), 1–2 or
numerous in 1(–3) rows
in epc
Also on outer walls; also in
culm, rhizome, achene
Duval-Jouve, 1873a; Pfeiffer, 1921b, 1927; Wille,
1926; Hryniewiecki & Kurtz, 1936; Mehra &
Sharma, 1965; Metcalfe, 1971; Schuyler, 1971;
Ollendorf et al., 1987; Tucker & Miller, 1990;
Deng, 1998; Oh & Ham, 1998
Fuireneae 5 2 C (C+sat), 1–5+ in epc;
plates, rods in epic
Also in culm, achene; in
wall sinuations
Duval-Jouve, 1873a; Pfeiffer, 1921b, 1927; Govin-
darajalu, 1969a; Metcalfe, 1971; Browning et
al., 1998
Eleocharideae 3 1 C+sat (elongated), 1–20+
in 1(–2) rows in epc
Si projections of vb sheath
cell walls; also in culm,
achene
Heiberg, 1867–1868; Schilling, 1918; Pfeiffer,
1927; Mehra & Sharma, 1963, 1965; Metcalfe,
1971; Govindarajalu, 1975; Menapace, 1991;
Deng, 1998
Abildgaardieae 6 5 C+sat (C, Nod), 1–4(–8)
in 1(–2) rows in epc
(Rarely in sinuations of anti-
clinal walls, epic); occa-
sionally in culm, achene
Rikli, 1895; Pfeiffer, 1927; Mehra & Sharma,
1965; Govindarajalu, 1966; Metcalfe, 1971;
Goetghebeur & Coudijzer, 1984, 1985; Deng,
1998
Cypereae 19 10 C+sat (Nod), 1–8(–10) in
1(–2) rows in epc (+ epic
in 1 genus & over vb
sheath in 1 genus)
Also in culm and achene Duval-Jouve, 1873a, 1873b; Rikli, 1895; Kaphahn,
1904–1905; Pfeiffer, 1920b; Mehra & Sharma,
1965; Metcalfe, 1971; Le Cohu, 1973; Denton,
1983; Norris, 1983; Sharma & Shiam, 1984;
Goetghebeur & Van den Borre, 1989; López &
Matthei, 1995; Deng, 1998
420 THE BOTANICAL REVIEW
Table IX, continued
Subfamily, tribe
No. of
genera
No.
studied
Type of silica, no. of bodies
per cell and location in leaf Notes References
Cyperoideae, continued
Dulichieae 3 2 C (C+sat), 1–5+ in epc Also in culm Pfeiffer, 1927; Hryniewiecki & Kurtz, 1936; Met-
calfe, 1971; Deng, 1998
Schoeneae 29 24 C (C+sat), (Nod, Pyr),
1–6–numerous in epc
(epic); C, cubical, rods,
warty, spicules (wedges),
1–3+ in epic; (C, 2+ in
par vb sheath)
Rods etc. in wall sinuations;
Also C on outer walls;
warty may be in pairs on
opposite sides of anticli-
nal walls; also in culm,
rhizome, root, achene
Duval-Jouve, 1873a, 1873b; Kaphahn, 1904–1905;
Pfeiffer, 1921b, 1921c, 1927; Wille, 1926;
Peisl, 1957; Norton, 1967; Govindarajalu,
1969b, 1975; Metcalfe, 1971; Ragonese et al.,
1984; Seberg, 1988; Browning & Gordon Gray,
1995; Ernst et al., 1995
Sclerioideae
Cryptangieae 4 4 C (C+sat), (domed), 1–4 in
1(–2) rows in epc/epic
Pfeiffer, 1921a, 1922, 1927; Metcalfe, 1971
Trilepideae 4 4 C (C+sat), (Nod), 1–numer-
ous in 1(–3) rows in epc
(epic)
May be 2 sizes; also in culm Pfeiffer, 1927; Chermezon, 1933; Metcalfe, 1971
Sclerieae 1 1 C (C+sat); warty, 1–3(–7)
in epc; Sph etc., 1–2 in
epic
Sph in pairs on opposite
sides of anticlinal walls;
Si particles in wall sinua-
tions; also in culm &
achene
Crüger, 1857; Pfeiffer, 1927; Mehra & Sharma,
1965; Metcalfe, 1971; Govindarajalu, 1975;
Franklin, 1979, 1981; Deng, 1998
Bisboeckelereae 6 4 C (C+sat), (Nod), 1–3+ in
epc; Sph, warty, 1–2(–3),
& particles in epic
Sph etc. in pairs on opposite
sides of anticlinal walls;
also Si in mesophyll
Pfeiffer, 1921b, 1927; Koyama, 1967; Metcalfe,
1971
Caricoideae
Cariceae 5 5 C+sat, (Nod), 1–6(+) in
1(–2) rows in epc (epic)
Rarely over sclerenchyma of
vb sheath; also in culm,
achene
Duval-Jouve, 1873a; Wilczek, 1892; Pfeiffer,
1921b, 1925, 1927; Wille, 1926; Hryniewiecki
& Kurtz, 1936; Mehra & Sharma, 1965;
Kukkonen, 1967; Metcalfe, 1971; Le Cohu,
1973; Walter, 1975; Toivonen & Timonen,
1976; Tallent & Wujek, 1983; Menapace &
Wujek, 1987; Crins & Ball, 1988; Waterway,
1990; Luceño, 1992; Deng, 1998, 2002; Oh &
Lee, 2001; Oh et al., 2001; Starr & Ford, 2001
SILICA BODIES IN MONOCOTYLEDONS 421
Fig. 5. Various silica body morphologies found in the order Poales and in Dasypogonaceae. A. Carex
intermedia (Cyperaceae), lateral view of a conical silica body with tiny spines projecting near the base
(bar = 10
m). B. Abildgaardia monostachya (Cyperaceae), conical bodies with satellites in epidermis
(bar = 10
m). C. Juncus inflexus (Juncaceae), silica sand in bundle-sheath cells (bar = 20
m). D. Juncus
arabicus (Juncaceae), silica sand in vascular bundle-sheath cells (bar = 10
m). E. Thamnochortus
floribundus (Restionaceae), an irregular or granular form of silica observed in epidermal cells (bar = 10
m). F. Anthochortus ecklonii (Restionaceae), spherical silica bodies overlying the sclerenchymatous
bundle sheath (bar = 10
m). G. Thurnia jenmanii (Thurniaceae), numerous small spherical/nodular
bodies in epidermal cells (bar = 10
m). H. Kingia australis (Dasypogonaceae), spherical silica bodies
with a rugose surface in epidermal cells (bar = 10
m). J. Dasypogon bromeliifolius (Dasypogonaceae),
epidermal silica sand (bar = 20
m).
422 THE BOTANICAL REVIEW
basal plate (Le Cohu, 1973), most frequently in one row per cell as seen in surface view but
sometimes in two or three rows. Silica cells often occur in longitudinal files; there is no differ-
entiation into long cells and short cells characteristic of Poaceae, with rare exceptions (bract of
Epischoenus villosus and Mesomelaena stygia). The number of bodies and rows per cell may
be diagnostic for a species, but there is always a range of values, and variation due to age of
leaf, environmental conditions, etc. must be taken into account (see Ollendorf, 1992). Each
large cone may be surrounded by a circle of small cones, termed “satellites,” as seen in surface
view; the extent to which satellites are developed tends to vary within a species.
A conical body may have two or more peaks, when it is transitional to the warty or nodular
type, which may be conical, spherical or irregularly shaped. In certain genera and species,
smooth or warty hemispherical bodies are formed on anticlinal walls of adjoining epidermal
cells; e.g., in Rhynchospora and Scleria (Govindarajalu, 1969b, 1975; Metcalfe, 1971). Other
types of body have been described as wedge shaped, often based on sinuations in the anticlinal
walls, or bridge shaped, when they traverse the cell lumina; these types are characteristic of
Hypolytreae. In certain genera, small silica particles, rods, plates or cubical bodies may occur,
especially in intercostal regions, where individual cells, including stomatal guard or subsidiary
cells and prickles, may be completely silicified.
Silica cells occur both adaxially and abaxially in the leaf epidermis, but the frequency varies
according to the number of subepidermal sclerenchyma strands or girders, which in some gen-
era are nearly equally numerous on both surfaces, while in others they are more numerous
abaxially (rarely adaxially). Silica bodies are sporadically present in intercostal regions of the
epidermis and rarely in mesophyll or diaphragm cells (e.g., in the leaf of Cladium articulatum:
Peisl, 1957). Kaphahn (1904–1905) noted silica bodies in parenchymatous cells overlying the
sclerenchymatous vascular bundle sheath and at borders of sclerenchyma girders in the leaf of
Cladium germanicum. They were seen in a similar position by Pfeiffer (1921b) in leaf and
culm of Cyperus mariscus.
Silica bodies, usually of similar type to those in the leaf, are present in the epidermis of leaf
sheath and culm and, rarely, in other positions; for example, in cells overlying vascular bundles.
Silica projections from parenchymatous bundle-sheath cell walls bordering air cavities were
observed in Eleocharis plantaginea culm by Schilling (1918) and Mehra and Sharma (1963).
Bodies have been observed infrequently in the rhizome (Wille, 1926) and rarely in the root
(e.g., in some exodermal cells of Rhynchospora spp.: Govindarajalu, 1975).
Wilczek (1892) was one of the first to investigate achenes of Cyperaceae for silica bodies.
He examined seven genera but found bodies only in Carex species, where there was one coni-
cal body per epidermal cell. More recently, several taxonomic studies have included observa-
tions of bodies in achenes, often using SEM; e.g., Bulbostylis (Goetghebeur & Coudijzer,
1985), Carex (Walter, 1975; Toivonen & Timonen, 1976; Wujek & Menapace, 1986; Menapace
& Wujek, 1987; Crins & Ball, 1988; Standley, 1990; Waterway, 1990; Luceño, 1992; Oh &
Lee, 2001; Oh et al., 2001; Starr & Ford, 2001), Eriophorum and Scirpus (Schuyler, 1971;
Tucker & Miller, 1990), Lipocarpha and related genera (Goetghebeur & Van den Borre, 1989),
Rhynchospora (Ragonese et al,. 1984) and Uncinia (Starr et al., 2003), although none was seen
in 3 species of Abildgaardia or 19 species of Fimbristylis (Goetghebeur & Coudijzer, 1984).
Table VIII shows the type and numbers of silica bodies in the leaf of tribes of Cyperaceae.
The data are taken mainly from Metcalfe (1971), but the observations for individual genera
have been regrouped according to Goetghebeur’s classification in Kubitzki (1998), to which
the numbers of genera refer. The conical type (⫾ satellites) is dominant in epidermal cells
overlying sclerenchyma in all tribes except Hypolytreae and Chrysitricheae, which together
constitute the Mapanioideae; here silica bodies are absent, restricted to small cones in sinuations
SILICA BODIES IN MONOCOTYLEDONS 423
of anticlinal walls, or wedge or bridge shaped, rarely of the typical conical type. The composi-
tion of the Mapanioideae has not changed since Clarke’s (1908) classification, except that
Syntrinema, with conical bodies, has been removed and included in Rhynchospora. The Cariceae
have also remained almost unaltered and are characterized by 1–5 or more conical bodies with
satellites per cell, sometimes in two rows.
An alternative suprageneric classification, based on cladistic analyses of 122 genera using
more than 300 morphological and other characters, was proposed by Bruhl (1995); he included
silica body type and position in culm and leaf among his characters, and his article should be
consulted for a full discussion of the differences between his classification and that of
Goetghebeur (1986).
Conical silica bodies are typical for most Cyperaceae, but they are not confined to this
family; for example, they are also present in some Orchidaceae and Arecaceae, although in the
two latter families there is usually only one body per cell, and they are never epidermal.
Although Prionium was traditionally placed either in Juncaceae or in its own family,
Prioniaceae (Munro & Linder, 1998), analyses of molecular data place it as sister to Thurniaceae
(e.g., Chase et al., 2000; Michelangeli et al., 2003). However, silica bodies are apparently
absent from Prionium and all Juncaceae apart from Juncus, which possesses silica sand in
vascular bundle-sheath cells (Figs. 5C, 5D), but present in Thurnia (Cutler, 1965, 1969) as
small, spherical bodies (Fig. 5G). Thus, this distribution of silica bodies may indicate two
separate losses of silica bodies in the sedge clade.
There is also at least one loss of silica bodies in the grass clade. Flagellaria, which pos-
sesses silica bodies, is sister to two subclades, one comprising Restionaceae and their allies; the
other, grasses and their allies. In the first subclade, three genera (Anarthria, Hopkinsia and
Lyginia) form a clade that is sister to Restionaceae. Hopkinsia and Lyginia are former
Restionaceae that were recently proposed as separate families, Hopkinsiaceae and Lyginiaceae
(Briggs & Johnson, 2000), since a molecular analysis (Briggs et al., 2000) found them to be
isolated from Restionaceae and sister to Anarthria (Anarthriaceae). Interestingly, all three gen-
era (Anarthria, Hopkinsia and Lyginia) apparently lack silica bodies.
Solereder and Meyer (1929) were the first to recognize silica bodies in Restionaceae, but
the first major anatomical study was by Cutler (1969); his observations were confirmed by
Linder (1984). Table VII is based on Cutler’s (1969) data, rearranged according to the classifi-
cation of Linder et al. (1998). Many genera are leafless, and most available data are for culms.
Silica bodies occur in the leaf or leaf base of a few species and occasionally in rhizomes but
have not been seen in roots. The recent taxonomy of Restionaceae is complex, with many
genera and species transferred to different taxa (Linder, 2000). Cutler’s (1969) work showed
that there were anatomical differences between African and Australian species that had previ-
ously been placed in the same genera; e.g., Restio and Leptocarpus. Certain species have sub-
sequently been transferred to other genera, so that there is now no genus with a distribution in
both South Africa and Australia. Silica is absent from several genera and from some species in
other genera. When present, silica is found in two main forms in Restionaceae: 1) granular
silica, usually filling cell lumina, in cells of parenchymatous sheath and central ground tissue
and occasionally in pillar cells, protective cells (see Cutler, 1969, for definitions of these terms)
and chlorenchyma but rarely in the epidermis (Fig. 5E); and 2) spherical-nodular bodies in
unspecialized cells or in stegmata, forming part of the parenchymatous bundle sheath or the
outer layer of the sclerenchymatous sheath (Fig. 5F). Stegmata have thickened, lignified or
suberized inner and anticlinal walls and thin outer walls. Both types may be present in one
species, and they occur in both South African and Australian species, as does absence of silica.
Cutler (1969) divided Lepyrodia species into two main groups based on anatomical characters,
424 THE BOTANICAL REVIEW
Fig. 6. Various silica body morphologies found in the epidermal cells of Poaceae. A. Aristida setigera,
costal dumbbell-shaped silica bodies (bar = 10
m). B. Brachiaria jubata, a form of silica intermediate
between the dumbbell-shaped form and the cross-shaped form (bar = 10
m). C. Apochiton burttii, cross-
shaped silica bodies (bar = 10
m). D. Aegilops triaristata, a horizontally elongated silica body with
sinuous outlines (bar = 10
m). E. Anthochloa lepidula, horizontally elongated bodies with smooth out-
lines (bar = 20
m). F. Astrebla squarrosa, saddle-shaped silica bodies (bar = 10
m). G. Agropyron
elongatum, a conical silica body (bar = 20
m).
one of which was the presence of granular silica alone in one group and spherical-nodular
bodies in the other group; species in the group with only granular silica have since been trans-
ferred to Sporadanthus. Silica bodies have not been observed in any species examined of
Staberoha or in the large genera Elegia and Chondropetalum.
In the other grass subclade (grasses and their allies), the bigeneric family Ecdeiocoleaceae
is putatively sister to Poaceae, with Joinvillea sister to this pair (Michelangeli et al., 2003).
Silica is present in all three families, although only as silica sand in culms of Ecdeiocolea
(Ecdeiocoleaceae). Silica bodies are present in most species of Poaceae, including Anomochloa,
Streptochaeta and Pharus, which are putatively sister to the rest of the family (GPWG, 2001).
There is a diverse range of silica bodies in Poaceae, including dumbbell-shaped, cross-shaped
SILICA BODIES IN MONOCOTYLEDONS 425
Table X
Distribution of silica bodies in Dasypogonaceae
Genus
No. of
species Type and location of silica References
Baxteria 1 Spherical silica bodies with rugose surface pres-
ent in leaf epidermal cells, generally one per
cell
Fahn, 1954; Rudall &
Chase, 1996
Calectasia 3 Fine silica sand or amorphous crystals present in
leaf epidermis
Rudall & Chase, 1996
Dasypogon 3 Fine silica sand or amorphous crystals present in
leaf epidermis
Rudall & Chase, 1996
Kingia 1 Spherical silica bodies with rugose surface,
present in the leaf epidermal cells, generally
one per cell
Fahn, 1954; Rudall &
Chase, 1996
intermediates between these two types, horizontally elongated shapes with smooth or sinuous
outlines, saddle shaped, conical shaped and numerous others (Figs. 6A–6G) (see Metcalfe,
1960). The distribution and structure of silica bodies in Poaceae will be discussed in more
detail in a separate publication.
4. Dasypogonaceae
The phylogenetic position of Dasypogonaceae within the commelinid clade remains equivo-
cal. For example, a relationship with palms was tentatively indicated by molecular data, but
without bootstrap support (Chase et al., 1995a, 2000; Givnish et al., 1999). Rudall and Chase
(1996) noted that habit and method of growth would support a relationship between
Dasypogonaceae and Arecaceae, but ovule structure and silica position and morphology indi-
cate an affinity with Rapateaceae. Within Dasypogonaceae (Table X), calcium oxalate crystals
are absent, but silica is present in all four genera (Rudall & Chase, 1996). In Kingia and Baxteria,
spherical (druse-like) silica bodies with a rugose surface are present in the leaf epidermal cells,
generally one per cell (Fig. 5H). These were previously reported by Fahn (1954) as druses
(clustered crystals of calcium oxalate), but X-ray and SEM examination effectively demon-
strated their silicaceous nature. Silica is also present in the epidermis of Dasypogon and
Calectasia in the form of fine silica sand or amorphous crystals, present in most epidermal cells
in Dasypogon (Fig. 5J) but less frequent in Calectasia.
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