ArticlePDF Available

Unusual morphological and anatomical features of two woody Madagascan endemics, Streptocarpus papangae and S. suffruticosus (Gesneriaceae), and their potential taxonomic value

Authors:

Abstract and Figures

As members of a small group of caulescent Madagascan endemics, Streptocarpus papangae and Streptocarpus suffruticosus are distinctive in being branched woody shrubs in a genus largely of herbaceous habit. The present study is the first detailed comparative investigation of any woody Madagascan Streptocarpus species and draws attention to certain notable morphological and anatomical characteristics, particularly their non-coherent anthers, foliar and stem sclereids, nodal anatomy (split-lateral or semi-girdling traces), and ovule morphology, features previously inadequately examined in Streptocarpus and their potential taxanomic value overlooked. For example, in a family where anatropous ovules were previously thought to be typical, the presence of hemi-anatropous ovules in Streptocarpus is confirmed and here recorded for the first time in the two species. Another feature is the occurrence of split-lateral traces, a distinctive nodal feature generally uncommon among angiosperms. Macrosclereids, rare among mainland African Streptocarpus have been observed in the stem, petiole, leaf lamina and receptacle of S. papangae but only near the base of the petiole in S. suffruticosus. The possible significance of these and other characters to the taxonomy and phylogenetic systematics of Streptocarpus is discussed.
Content may be subject to copyright.
Unusual morphological and anatomical features of two woody Madagascan
endemics, Streptocarpus papangae and S. suffruticosus (Gesneriaceae), and
their potential taxonomic value
K. Jong, F. Christie, J.-H. Paik
1
, S.M. Scott, M. Möller
Royal Botanic Garden Edinburgh, 20A Inverleith Row, Edinburgh EH3 5LR, Scotland, UK
Received 9 May 2011; received in revised form 3 February 2012; accepted 8 February 2012
Abstract
As members of a smallgroup of caulescent Madagascan endemics, Streptocarpus papangae and Streptocarpus suffruticosus are distinctive in being
branched woody shrubs in a genus largely of herbaceous habit. The present study is the rst detailed comparative investigation of any woody
Madagascan Streptocarpus species and draws attention to certain notable morphological and anatomical characteristics, particularly their non-
coherent anthers, foliar and stem sclereids, nodal anatomy (split-lateral or semi-girdling traces), and ovule morphology, features previously inadequate-
ly examined in Streptocarpus and their potential taxanomic value overlooked. For example, in a family where anatropous ovules were previously
thought to be typical, the presence of hemi-anatropous ovules in Streptocarpus is conrmed and here recorded for the rst time in the two species.
Another feature is the occurrence of split-lateral traces, a distinctive nodal feature generally uncommon among angiosperms. Macrosclereids, rare
among mainland African Streptocarpus have been observed in the stem, petiole, leaf lamina and receptacle of S. papangae but only near the base of
the petiole in S. suffruticosus. The possible signicance of these and other characters to the taxonomy and phylogenetic systematics of Streptocarpus
is discussed.
© 2012 SAAB. Published by Elsevier B.V. All rights reserved.
Keywords: Hemi-anatropous ovules; Leaf structure; Non-cohering anthers; Ovule starch pattern; Sclereids; Shoot structure; Split-lateral traces
1. Introduction
Streptocarpus Lindl. (Gesneriaceae) consists of ca. 140 spe-
cies (Weber, 2004). Its centre of distribution is southern Africa,
its range extending into East and West tropical Africa (Hilliard
and Burtt, 1971). A few species of doubtful affinity have been
recorded from Asia. Thirty-seven species are endemic to Mada-
gascar and the Comoro Islands (Hilliard and Burtt, 1971;
Humbert, 1971). A diversity of growth forms, many of highly un-
usual architecture, occurs in the genus, ranging from the familiar
acaulescent rosulate Streptocarpus rexii (Hook.) Lindl. (Cape
Primrose) and single-leafed Streptocarpus grandis N.E.Br. to
caulescent species, such as Streptocarpus caulescens Vatke
with opposite decussate leaves borne on aerial shoots (Hilliard
and Burtt, 1971; Jong, 1970, 1973, 1978; Jong and Burtt, 1975).
A greater morphological diversity, however, is now known
among Madagascan members of Streptocarpus through the
work of Humbert (1955, 1967, 1971) and Hilliard and Burtt
(1971). Some of the species there have a rosette growth habit
with long-petioled leaves, bearing a striking resemblance to
Saintpaulia H.Wendl. (African violet) of mainland Africa
(Hilliard and Burtt, 1971; Humbert, 1971; Möller and Cronk,
2001a), but more spectacular are the woody species.
Species with a shrubby woody habit are rare in the genus and
form only a small group of seven species endemic to Madagascar:
Streptocarpus campanulatus B.L.Burtt, Streptocarpus coursii
Humbert, Streptocarpus glabrifolius Humbert, Streptocarpus
macropodus B.L.Burtt, Streptocarpus papangae Humbert,
Corresponding author. Tel.: +44 131 2482886; fax: +44 131 2482901.
E-mail address: m.moeller@rbge.org.uk (M. Möller).
1
Current address: Korea Research Institute of Bioscience and Biotechnology,
Gwahak-ro 125, Yuseong-gu, Daejeon, Republic of Korea, 305-806.
0254-6299/$ -see front matter © 2012 SAAB. Published by Elsevier B.V. All rights reserved.
doi:10.1016/j.sajb.2012.02.004
Available online at www.sciencedirect.com
South African Journal of Botany 80 (2012) 44 56
www.elsevier.com/locate/sajb
Streptocarpus suffruticosus Humbert, and Streptocarpus tsarata-
nanensis B.L.Burtt (Hilliard and Burtt, 1971; Humbert, 1971). As
little detailed anatomical information is available for any such
members of the genus, S. papangae and S. suffruticosus,the
only two representatives successfully cultivated at the Royal
Botanic Garden Edinburgh (RBGE), form the subject of this
investigation. Both occur in montane evergreen forest, and S.
papangae is also found among ericoid shrubs on mountain
tops. S. papangae is known only from the Col de Beampingaratra
inSouthMadagascar,growingasashrubupto120cm,
whereas S. suffruticosus occurs in central, northern and east-
ern Madagascar as shrubs 12m tall (Hilliard and Burtt,
1971). With regard to the latter our own field observations in
the North indicate that it occurs mainly as an epiphyte.
Streptocarpus comprises two subgenera, Streptocarpella
consisting of caulescent species and Streptocarpus of predominant-
ly acaulescent ones. The woody species have thus been placed in
the subgenus Streptocarpella by Hilliard and Burtt (1971), but
they differ in so many respects from other members of this subge-
nus that their assignment may have to be re-evaluated when more is
known about them. In their book on the genus, Hilliard and Burtt
(1971, chapter 9) allocated a separate chapter to Madagascan
Streptocarpus,recognising three groupings that are not repre-
sented on the mainlandplacing together the shrubby woody spe-
cies into their group (iii) characterised by short filaments, with
seeds long pointed at both ends and distinctly larger than in the
other species(Hilliard and Burtt, 1971).
Phylogenetic studies on Streptocarpus have increased our un-
derstanding of the evolution of the genus (Möller and Cronk,
1997; Smith et al., 1998) and demonstrated that woody Madagas-
can species are not closely related to herbaceous caulescent ones
(Möller and Cronk, 2001a,b; MacMaster et al., 2005). Molecular
phylogenetic work indicated that the subgenus Streptocarpella is
not a monophyletic group, with only the African and Madagascan
herbaceous caulescents forming a closely related alliance (clade I
in Möller and Cronk, 2001a,b). All acaulescents of subgenus
Streptocarpus, fall in clade II of Möller and Cronk (2001a,b).
The woody caulescent species also fell in this clade (Möller and
Cronk, 2001a,b; MacMaster et al., 2005). The two clades are
fully congruent with the basic chromosome number, being
x=15 for the caulescent members in clade I, and x = 16 for the
acaulescent species in clade II (Möller and Cronk, 2001a). It
should be noted that the shrubby caulescent Madagascan species
S. papangae and S. suffruticosus also have x=16 (Jong and
Möller, 2000; Möller and Kiehn, 2004). Within clade II these
species form a monophyletic clade that is most closely related
to acaulescent Madagascan species, such as Streptocarpus
ibityensis Humbert, Streptocarpus itremensis B.L.Burtt and
Streptocarpus lanatus MacMaster (Möller and Cronk, 2001a,b;
MacMaster et al., 2005). Thus, it seems that members of the
shrubby woody group constitute a coherent group, separate
from herbaceous caulescent species of both Madagascar and
mainland Africa; their evolutionary and morphological affinities
may lie with other Madagascan acaulescent species.
Apart from their shrubby habit and similarity in basic chro-
mosome number noted above, S. papangae and S. suffruticosus
are clearly distinguishable anatomically from each other, as for
example differences in the abundance and distribution of scler-
eids, structure of stomata and indumentums (Hilliard and Burtt,
1971). These features, together with new observations on other
aspects of shoot, floral and ovular structure are highlighted in
the present study, alongside a consideration of their relevance
and potential value to the taxonomy of the woody species and
the genus.
2. Materials and methods
2.1. Plant materials
This investigation was based on specimens cultivated at the
RBGE. Two genotypes of S. papangae were examined, one
with dark pink flowers (four individuals), the other creamy
white (six individuals) (Möller 9718, E, cult. RBGE 19972886
referred to as A and B, respectively). One accession with eight
plants of S. suffruticosus var. suffruticosus was available for
study (Möller 9877, E, cult. RBGE 19990122).
S. papangae was propagated from cuttings collected at the
Col de Beampingaratra, whereas S. suffruticosus was raised
from seed, collected on the Marojejy Mountains, Madagascar.
The accessions thrived in cultivation; at the time of writing,
specimens of S. papangae have reached ca. 140 cm in height,
with several woody branches arising from the base, and often
flowering profusely. S. suffruticosus has a pendulous form,
conforming to its epiphytic habit in the wild. For the benefit
of horticulturists interested in growing these unusual plants,
some notes on their cultivation are appended. Both species, in-
terestingly, failed so far to set seed under glasshouse condi-
tions, despite numerous attempts at artificial pollination.
2.2. Preparation of stem, node and leaf sections
Freshly collected shoot samples were fixed in FAA (9 parts
70% ethanol, 0.5 parts glacial acetic acid and 0.5 parts formal-
dehyde, Johansen, 1940) or in Farmer's Fluid (3 parts absolute
ethanol to 1 part glacial acetic acid, Johansen, 1940) for 1 h to
overnight, then stored in 70% ethanol for later use. No notable
difference in fixation was detected between the two fixatives.
Observations were made on free hand sections of stem and
nodes as well as on freezing microtome sections. Rotary micro-
tome sections of paraffin wax-embedded stem and leaf material
were prepared after dehydration in a tertiary butyl alcohol series
according to the procedure in Johansen (1940), except for the
substitution of the toxic xylene with Histoclear in the final
steps. Parawax of 56 °C melting-point was used in embedding.
Microtome sections were taken at 1215 μm, and stained with
dilute aqueous Safranin O (0.05%) (Johansen, 1940).
Fixed material for clearing of nodes was transferred to water
(through an alcohol series). Thick longitudinal as well as trans-
verse sections were then placed in 5% NaOH at 3040 °C for 5
or more days, washed in several changes of distilled water and
transferred to saturated chloral hydrate until the material was
transparent. The vascular tissues became clearly visible, al-
though staining (about 5 min) in 0.01% aqueous Safranin O im-
proved the details.
45K. Jong et al. / South African Journal of Botany 80 (2012) 4456
Cleared material was viewed under incident light against a
dark background under a Stemi 2000C dissecting microscope
(Zeiss, Welwyn Garden City, UK) and photographed with an
AxioCam MRc5 digital camera. Microtome sections were
viewed under a Zeiss Axioskop brightfield microscope and im-
ages recorded with a similar digital camera as above.
2.3. Preparation of ovary and anther sections
Freshly collected floral samples were fixed in FAA as above
(with 50% ethanol instead of 70% for the more delicate materi-
al). Rotary microtome sections of plastic-embedded material
(Technovit 7100, Heraeus Kulzer, Wehrheim, Germany) were
prepared according to the manufacturer's protocol, and sec-
tioned at 10 μm. Sections were double-stained with Delafield's
Haematoxylin and dilute Safranin O according to the rapid
technique of Jong (1970) that is essentially similar to the proto-
col of Dean (1940). The microtome sections were observed
with an Axioskop brightfield microscope and the images were
captured as above.
2.4. Whole mounts of ovules
Newly opened flowers fixed in Farmer's Fluid were first trans-
ferred to distilled water through an ethanol series. An ovary
segment was then placed in a drop of water on a microscope
slide, one side cut open longitudinally to expose the ovules.
Under a dissecting microscope, ovules were carefully detached
with a dissecting needle or pointed scalpel, unwanted tissues re-
moved, excess water blotted off, and a drop of Melzer's Reagent
applied (see below). The material was left for about 5 min before
applying a coverslip, and sealing it with rubber solution or clear
nail varnish. The preparations were observed under a brightfield
Axioskop microscope and the images were recorded as above.
Melzer's Reagent is basically a mycological reagent first intro-
duced by Melzer in 1924. It was adopted as a routine histological
mountant by Jong (1970) and now found to be of great advantage
to the present study. In addition to the staining of cellulose cell
walls a yellow colour, and lignified tissues a light to darker or-
ange hue, Melzer's chloral hydrate component conferred a useful
degree of clearing, while its iodine and potassium iodide ingredi-
ents revealed the presence of starch. As this reagent is not widely
used in angiosperm histology, its composition as published in
Wakefield and Dennis (1950, p. 37) is here included: distilled
water 100 ml, chloral hydrate 100 g, potassium iodide
5 g, and iodine 1.5 g. One of the drawbacks of this reagent
is that the reactions observed, particularly the starch reaction,
fade within 5 days or so. It is therefore advisable to photograph
suitable views soon after slide preparation.
2.5. Scanning electron microscopy of leaves and floral
structures
Freshly collected leaf and floral samples were fixed in 50%
ethanol FAA overnight at room temperature, then dehydrated
through an ethanol series: 15 min at 50%; 15 min at 70%;
10 min at 95%; 5 min at 100%; 2×5 min at 100% dry acetone.
They were then dried using an Emitech K850 critical point
dryer (Quorum Technologies Ltd, Ashford, UK). Ovules were
first dissected from the ovary using a razor blade prior to fixa-
tion to assist their handling once dry. Samples were mounted on
aluminium stubs with double sided sticky carbon tabs and coat-
ed with platinum for 2 min at 25 mA using an Emitech K575x
sputter coater (Quorum Technologies Ltd, Ashford, UK). The
material was scanned using a LEO Supra 55VP SEM (Zeiss,
Cambridge, UK). Images were captured at 5 kV using secondary
electron signal detection.
3. Observations
Although S. papangae and S. suffruticosus are remarkable in
being woody shrubs (Fig. 1A, B) in a largely herbaceous genus,
they possess other distinctive morphological and anatomical
characteristics. While they have some features in common, they
also differ in numerous notable respects from each other, not
only in gross morphology, but also in their anatomy (summarized
in Table 1). To avoid unnecessary repetition, characteristics for S.
papangae are given in fuller detail than those for S. suffruticosus
and generally only where they differ from S. papangae.
Stems erect (S. papangae,Fig. 1A) or pendulous (S. suffru-
ticosus,Fig. 1B), almost glabrous, inconspicuous eglandular
trichomes on the first and second internodes (S. papangae)or
densely pubescent with predominantly long uniseriate multicel-
lular glandular and eglandular trichomes, and some scattered
short two-celled glandular ones (S. suffruticosus); young inter-
nodes slightly flattened, older ones cylindrical (S. papangae)or
shoots always round (S. suffruticosus); white patches at nodes
often containing stomata; periderm superficial with lenticels
in both species; in transverse sections (TS), stem cortical cells
not in a neatly layered organisation (Fig. 2A); outer cortex of
6 or 7 layers of collenchyma (S. papangae) or 7 or 8 neatly lay-
ered rectangular parenchyma cells (S. suffruticosus); simple
starch grains in the parenchyma and endodermis, notably abun-
dant in cortical layers adjoining the endodermis (S. papangae)
or simple starch grains present in cortical tissues as well as in
endodermis and pith (S. suffruticosus); Casparian strip indis-
tinct in places; sclereids scattered in outer cortex, simple, rhom-
boidal to oblong (S. papangae)(Fig. 2B, C) or sclereids absent
(S. suffruticosus); druses and other forms of crystals in pith;
vascular bundles (with pericyclic fibre caps) initially separate
become joined by lignified interfascicular tissue.
Nodes trilacunar with split-lateral traces, i.e. in addition to a
single median leaf trace that enters the associated leaf directly,
two lateral traces arising 90° from the leaf insertion point, each
partially encircling or girdling the stem before reaching the leaf
it supplies. In both species, these laterals can arise through bi-
furcation of a single vertical trace at the level of leaf insertion
(Fig. 3A, B) or as parallel vertical traces running down the in-
ternode (Fig. 3C, D); median trace with prominent associated
single gap (Fig. 3E); lateral trace gaps small and often indistinct
(Fig. 3B); split-lateral traces observed in both young and old
nodes; sclereids abundant in the outer regions, with their long
axes parallel to the stem axis (S. papangae)(Fig. 2C) or sclereids
absent (S. suffruticosus).
46 K. Jong et al. / South African Journal of Botany 80 (2012) 4456
Leaves opposite decussate, petioles 1020(30) mm long (S.
papangae)or1015 mm long (S. suffruticosus); lamina
115160 × 4060 mm (S. papangae)or65100 × 3040 mm
(S. suffruticosus); unequal at base; thick, coriaceous, largely
glabrous except for a few glandular trichomes, each with a
single-celled stalk and one to four-celled heads in depressions
on both upper and lower epidermis (Fig. 5E), only a few incon-
spicuous multicellular eglandular trichomes on petioles, some-
times on young leaves of the first and second nodes (S.
papangae)(Figs. 4A; 5A, C) or thin (Fig. 4B), densely pubes-
cent with long trichomes, uniseriate multicellular glandular and
eglandular (tipped with a thick-walled pointed terminal cell),
trichome-base with conspicuous multicellular foot (Fig. 5B),
some short glandular ones scattered among the long glandular
ones on both surfaces (S. suffruticosus)(Fig. 5D, F); leaf mar-
gins smooth, gently undulating, with inconspicuous hydathodes
(S. papangae) or finely toothed, each tooth with a conspicuous
hydathode (S. suffruticosus); adaxial epidermal cells mostly of ir-
regular isodiametric shape, surface conspicuously convex (S.
papangae)(Figs. 4A; 5A) or with flat surface (S. suffruticosus)
(Fig. 5B); stomata adaxially absent; abaxial epidermis glabrous,
cells not convex (S. papangae) or obscured by the dense presence
of trichomes and stomata (S. suffruticosus)(Fig. 5D); stomata ani-
socytic with three unequal subsidiary cells surrounded by an addi-
tional ring of larger narrow subsidiary cells (S. papangae)(Fig. 5C)
or anisocytic stoma conspicuously raised on usually two to three
rings of subsidiary cells of varying size (S. suffruticosus)
(Figs. 4B, C; 5D, F); lamina 450500 μmthick(S. papangae)or
300350 μm(S. suffruticosus); hypodermis a single layer in geno-
type with cream-coloured flowers, two in genotype with pink
flowers (S. papangae)(Fig. 4A), number of layers constant within
a plant irrespective of leaf age, sclereids present in the inner layer
1mm
1mm 1mm
G
1mm
10cm
10cm
a
1cm
p
A
BF
ED
C
Fig. 1. General morphology. Streptocarpus papangae: (A) habit; (C) much branched sympodial inflorescence; (D) front view and (E) side view of the pink flower, note
glabrous calyx; (F) front view of the creamy white flower showing non-coherent anthers. Streptocarpus suffrutic osus: (B) habit; (G) flower, note dense pubescence. a
anther, p peduncle.
47K. Jong et al. / South African Journal of Botany 80 (2012) 4456
with long axes perpendicular to epidermis, also abundantly in the
midrib and the outer regions of the petiole (S. papangae)
(Figs. 3B; 4A, D) or hypodermis absent (S. suffruticosus); palisade
single layer; spongy mesophyll ca. 250 μm thick, with scattered
astrosclereids that resemble lignified mesophyll cells (S. papangae)
(Fig. 4E) or ca. 150 μm thick, lower epidermal cells with abundant
simple starch grains, sclereids notably confined to basal region of
petiole, slightly longer than short, otherwise not very different in
size from the surrounding parenchyma (S. suffruticosus)
(Figs. 2D; 3B, D).
Inflorescences axillary in the upper part of the shoot (Fig. 1A),
branching repeatedly and symmetrically up to eight levels of
dichasial cymose units (Fig. 1C), fully developed inflorescence
carries remarkably about 500 flowers (at least in cultivated spec-
imens; few-flowered in the field according to the description of S.
papangae in Hilliard and Burtt, 1971). Peduncles 7090 mm
long (S. papangae)or2040 mm long (S. suffruticosus); pedicels
ca. 68 mm long, obliquely attached to flowers (S. papangae)
(Fig. 1E) or ca. 6 mm long, straight attachment to flowers
(S. suffruticosus); trichomes few, inconspicuous, multicellular
eglandular on lower regions of inflorescence, on bracts and brac-
teoles (S. papangae) or on peduncle and pedicel long, uniseriate
multicellular glandular and eglandular, some short, glandular,
scattered among long ones (S. suffruticosus).
Calyx lobes narrowly linear-lanceolate (S. papangae)(Fig. 1E)
or lanceolate (S. suffruticosus); ca. 3 mm long (S. papangae)orca.
4mm long (S. suffruticosus); a few short one to four-celled
glandular (S. papangae) or long glandular and eglandular multi-
cellular trichomes (S. suffruticosus); sclereids scattered in recepta-
cle (S. papangae)orabsent(S. suffruticosus).
Corolla pouch-like (Fig. 1DG); glabrous; short corolla tube
ca. 45 mm long, corolla face ca. 78mmwide (S. papangae)
or ca. 68mmwide(S. suffruticosus); in some plants dark pink
(Fig. 1D, E), creamy white (Fig. 1F) in others (S. papangae)or
light pink (S. suffruticosus)(Fig. 1G); lobes reflexed.
Stamens 2, in anterior positions; filaments short, 1 mm long
(S. papangae)(Fig. 5G) or ca. 11.5 mm long and each with a
prominent apical tooth (S. suffruticosus)(Fig. 5H); free to base;
glabrous; anthers non-coherent, each situated on either side of
the ovary (Figs. 1F, 5G, H); filaments short, curved, arising
from a pad of tissue at the corolla base; initially separate pollen
sacs becoming confluent at maturity; wall layers comprise the
epidermis, one middle layer, a typical endothecium with sec-
ondary thickening and single layered tapetum; stomium sub-
apical; introrse dehiscence (Figs. 5H, 6A); staminodes 2
(Fig. 5G, H).
Ovary bottle-shaped, ca. 2.5 mm long (S. papangae)(Fig. 5G)
or ca. 1.5 mm long (S. suffruticosus)(Fig. 5H); glabrous (S.
papangae) or with short multicellular glandular trichomes similar
to those on leaves (S. suffruticosus)(Fig. 5H); unilocular; bifid
intrusive parietal placenta at right angles to the dorso-ventral
floral axis; ovules only at tips of the incurved placental surface
(Fig. 6B); nectary disc a ring.
Style ca. 2.5 mm long (S. papangae) or ca. 3 mm long (S.
suffruticosus). Stigma stomatomorphic with a deep cleft; sub-
spatulate (S. papangae)(Fig. 5I) or sublingulate, somewhat bi-
laterally flattened (S. suffruticosus)(Fig. 5J); surface papillate;
papillae bottle-shaped, dimple-tipped with callose, covering
only ca. 200 μm length at the tip (S. papangae)(Fig. 5I) or pa-
pillae covering relatively larger stigmatic area ca. 800 μm(S.
suffruticosus)(Fig. 5J).
Ovules hemi-anatropous, micropyle facing obliquely out-
wards (Fig. 6C); ovules straight (S. papangae)(Fig. 6D) or with
slightly curved micropyle (S. suffruticosus)(Fig. 6E); integument
single; funiculus short; in newly opened flowers ovules with a
regular pattern of starch granule distribution in the shape of anex-
clamation mark, showing distinct polarity, the greatest quantity of
Table 1
Morphological and anatomical differences between the shrubby Madagascan
Streptocarpus papangae and S. suffruticosus.
Character S. papangae S. suffruticosus
Gross
morphology
Erect terrestrial shrub;
glabrous
Pendulous epiphyte;
densely pubescent
Stem and node
Sclereids Present Absent
Internodes 1st and 2nd somewhat
flattened
Always round
Leaf
Petiole 1020(30) mm long 1015 mm long
Lamina 115160 × 4060 mm 65100 × 3040 mm
Thickness 450500 μm 300350 μm
Spongy
mesophyll
Ca. 250 μm thick Ca. 150 µm thick
Margins Smooth, with inconspicuous
hydathodes
Finely toothed, each tooth
with a conspicuous hydathode
Trichomes Scattered short glandular
trichomes on both leaf surfaces
Dense indumentum of long
glandular and eglandular
trichomes on both surfaces
Adaxial
epidermis
Cell surface distinctly convex Cell surface flat
Stomata Level with epidermal cells Raised on turrets
Hypodermis One or two layers Absent
Sclereids In the hypodermis, midrib and
outer regions of the petiole;
astrosclereids in spongy
mesophyll
Confined to basal region
of petiole
Floral features
Peduncle 7090 mm long 2040 mm long
Pedicel Ca. 68 mm long, obliquely
attached to flowers
Ca. 6 mm long, with
straight attachment to flowers
Trichomes Few short glandular trichomes
on the lower region of
inflorescences, on bracts
and bracteoles
Peduncle and pedicel densely
pubescent, long uniseriate
multicellular glandular and
eglandular trichomes; some
short glandular trichomes
scattered among long ones
Calyx lobes Ca. 3 mm long, some short
glandular trichomes on
outer surface
Ca. 4 mm long, long glandular
and eglandular multicellular
trichomes on outer surface
Sclereids Present in receptacle Absent
Stamens Filament ca. 1 mm long,
without apical tooth
Filament ca. 11.5 mm long,
each with apical tooth
Stigma Subcapitate Sublingulate
Ovary Ca. 2.5 mm long,
bottle-shaped, glabrous
Ca. 1.5 mm long, with short
multicellular glandular
trichomes
Ovules Straight micropylar tip Slightly curved micropylar tip
48 K. Jong et al. / South African Journal of Botany 80 (2012) 4456
starch at micropylar end, sparser towards the chalaza, usually fol-
lowed by a clear zone, ending in a small dot-like group (Fig. 6D,
E); starch granules mainly compound at the micropylar pole,
much larger than those at the chalazal end where the grains tend
to be simple; in microtome sections, starch grains clearly visible
within the embryo-sac itself as well as in the nucellus (Fig. 6C).
4. Discussion
4.1. Secondary growth
Woodiness is perhaps the feature that clearly differentiates
the shrubby Madagascan species examined here from any
other group of Streptocarpus species recognised by Hilliard
and Burtt (1971). Secondary growth through the activity of a
vascular cambium, however, is not unique to S. papangae and
S. suffruticosus, as it also occurs in other caulescent but non-
shrubby Streptocarpus, as for example in the herbaceous peren-
nial S. caulescens and annual Streptocarpus nobilis C.B.Clarke
of mainland Africa (Jong, 1970). In her study of the former,
Sahasrabudhe (1970) observed that secondary growth is re-
stricted to the vascular bundles of the eustele. Secondary tissues
are also formed to a limited extent in acaulescent species, as in
the unifoliate S. grandis (Jong, 1970; Schenk, 1942). The
woodiness of the two Madagascan shrubs is clearly the result
of the relatively larger amounts of secondary vascular tissue
formed. Woodiness is a character shared by all shrubby Mada-
gascan species, and since they appear to form a natural group
(MacMaster et al., 2005), this character is diagnostic for these
species.
4.2. Indumentum
The indumentum is probably the most variable character in
plants. While Solereder (1908) subdivided the trichomes of
Gesneriaceae into two categories, glandular and eglandular,
Sahasrabudhe and Stace (1974) distinguished five categories,
(1) short glandular trichomes, (2) stalked glandular trichomes,
(3) unbranched eglandular trichomes, (4) branched eglandular
trichomes and (5) seedling glandular trichomes. The trichomes
of the two woody Streptocarpus species here conform to the
above first three categories. However, even though they have
many characters in common (e.g. non-coherent anthers, chromo-
some number and woodiness) and are phylogenetically closely
related to each other (MacMaster et al., 2005), they differ mark-
edly in their indumentums (Table 1). This difference is of
diagnostic value, though its ecological significance is unclear;
S. papangae is a terrestrial plant in ericoid shrubland whereas S.
suffruticosus a facultative epiphyte in evergreen rainforest.
However, many other evergreen rainforest epiphytes are gla-
brous, as in most species of the genus Aechynanthus Jack of the
Gesneriaceae.
The basal cells of the uniseriate trichomes of S. suffruticosus
are distinctly multi-celled, a feature that occurs also in other
Gesneriaceae, as for example in the New World species such
as Kohleria grandiflora L.P.Kvist & L.E.Skog (as Capanea
grandiflora in Wiehler, 1983). The glandular trichomes of S.
suffruticosus produce a sticky exudate, also visible as yellow-
brown droplets in Melzer stained preparations. Short glandular
trichomes situated in depressions on the adaxial leaf surface en-
countered in S. papangae (Fig. 5A, C) have also been reported
for some Aeschynanthus species (e.g. Aeschynanthus parvifolius
200µm
200µm
l
pe
cvb
200µm
sc
llt
1000µm
llt
A
CD
B
Fig. 2. Shoot anatomy and sclereid distribution. Streptocarpus papangae: (A) transverse sections of a young stem with superficial periderm and lenticel, outer cortex
and arrangement of vascular bundles; (B) stem longitudinal section of the fourth node showing sclereid (stained red) distribution in the cortex and petioles, and split-
lateral traces; (C) longitudinal section of the fourth node with sclereids (stained red). Streptocarpus suffruticosus: (D) longitudinal section of the fourth node base of
the petiole showing split-lateral trace, sclereids only in the petiole base (arrows). l lenticel, llt lateral leaf trace, c cortex, pe periderm, sc sclereids,
vb vascular bundle.
49K. Jong et al. / South African Journal of Botany 80 (2012) 4456
R.Br.) (Metcalf and Chalk, 1950) and the Sri Lankan Championia
reticulata Gardner, Chirita D.Don and Didymocarpus Wall.
(Herat and Theobald, 1979). The species from Sri Lanka of the lat-
ter two genera are now included in Henckelia Spreng. (Weber et
al., 2011). Too few observations across the Gesneriaceae are avail-
able to make any sound deduction on the systematic value of these
indumentum features.
4.3. Stomata
Both the Madagascan species studied here possess basically
anisocytic stomata. As the three unequal subsidiary cells are
surrounded by one or more rings of narrow cells, these stomata
may be classified as cyclocytic in the terminology of Stace
(1965). The characteristic domed structures topped by a single
stoma above a large substomatal chamber in S. suffruticosus
(Figs. 4B, C; 5D, F), termed stomatal turretsby Hilliard
and Burtt (1971), are clearly very different from those of S.
papangae, where the stomata are more or less level with the
epidermis.
Turrets with a single stoma similar to those of S. suffruticosus
are also found in New World Gesneriaceae, in most members of
the tribe Gloxinieae (e.g. Kohleria Regel and Moussonia Regel,
Wiehler, 1983) and in a few of the Old World, for example
Henckelia humboldtiana (Gardner) A.Weber & B.L.Burtt,
Henckelia floccosa (Thwaites) A.Weber & B.L.Burtt and the
monotypic Championia reticulata (Herat and Theobald, 1979).
Stomatal turrets consisting of groups of stomata instead of just
a single stoma have been reported in a few species of the Old
World (e.g. Boea Lam., Cyrtandra J.R.Forst. & G.Forst and on
the petiole-like structure (petiolode in the terminology of Jong,
1970) of the unifoliate S. grandis) and the New World (e.g.
Napeanthus Gardner and the Gesneria alliance) (Jong, 1970;
Sahasrabudhe and Stace, 1974; Skog, 1976). The occurrence of
500µm
mltg
llt
llt
vc
llt
llt
mlt
500µm
mlt
llt
llt
vc
llt
500µm
mlt mlt
500µm
mlt mlt
llt
500µm
llt
mlt mlt
A
C
DE
B
Fig. 3. Shoot vasculature. Streptocarpus papangae: (A) longitudinal section through young stem observed from the outside, median leaf traces and split-lateral leaf traces
with split configuration. Streptocarpus suffruticosus: (B) longitudinal section through the fourth node external view, showing medianleaf traces and split-lateral leaf traces
with split configuration and sclereids at the base of the petiole (arrowheads); (C) young node with median leaf traces and split-lateral leaf traces with parallel configuration;
(D) transverse section of the 4th node with the median leaf and split-lateral leaf traces in parallel configuration, and band of sclereids only at the base of the petioles
(arrowheads); yellow line indicates the plane of sectioning of the stem shown in E; (E) stem longitudinal section at the fourth and fifth node internal view, showing a spatial
relationship between the median leaf traces and the split-lateral leaf traces, split configuration with continuing vascular strands. llt lateral leaf trace, mlt median leaf
trace, mltg median leaf trace gap, vc vascular cylinder.
50 K. Jong et al. / South African Journal of Botany 80 (2012) 4456
such stomata in a wide range of genera across the family suggests
that they may have evolved several times independently. The
most recent molecular phylogenetic study clearly supports this
inference, as the above-mentioned genera of both the Old
World and the New World belong to unrelated major clades
(Möller et al., 2009).
4.4. Hypodermis
In the Gesneriaceae the hypodermis is generally regarded as
the water storage tissue (Metcalf and Chalk, 1950; Rosser and
Burtt, 1969; Wiehler, 1983). Within a genus its presence can
be consistent but the number of layers can vary greatly, and
was found for example, to be between one and nine layers
among 32 species of Aeschynanthus analysed by Rosser and
Burtt (1969).
The presence or absence of hypodermal layers has been
reported for the genera in both Old World and New World
(Metcalf and Chalk, 1950; Sahasrabudhe, 1970; Wiehler,
1983), reflecting Cutler's view that because of the sporadic
occurrence of the distinct hypodermis in the taxa of vascular
plants, its presence or absence is of little taxonomic and small
diagnostic value (except at the species level)(Cutler et al.,
2007, p. 61). And although Wiehler (1983) suggests that the
absence/presence of a hypodermis can have a taxonomic value
in separating genera such as Alloplectus Mart. and Nematanthus
Schrad. and Alsobia Hanst. from Episcia Mart., he gives exam-
ples of variation within a genus as in Gloxinia. This was also
found for Streptocarpus by Sahasrabudhe (1970) who showed
that all acaulescent species she examined lack a hypodermis, but
not all caulescent herbaceous species possessed a hypodermis. No-
tably it was absent in the African S. nobilis and the Madagascan
Streptocarpus hilsenbergii R.Br. We only investigated two
woody Madagascan species here, and these differ in the presence
of a hypodermis. This illustrates the low diagnostic value of this
characteristic for this group of Streptocarpus species.
4.5. Split-lateral leaf traces
Girdling traces are generally uncommon among vascular plants.
They are characteristic of cycads but otherwise not known in other
gymnosperms (Crane, 1985). They have been recorded in just a
few angiosperm families (Dickison, 1980; Howard, 1970; Puff,
1978).
Among the first studies on the nodal pattern of such lateral
traces specifically in the family Gesneriaceae was in fact that of
Hollstein. His work was contained in his unpublished dissertation
in 1878 which was traced by Wiehler (1983) to the only known
copy in the Library of Congress, Washington DC. Wiehler's
(1983) own extensive nodal survey covered over 340 species
largely of neotropical Gesneriaceae, confirming the presence of
split-lateral traces only in members of the tribe Episcieae. The
nodal pattern in all samples from other tribes was unilacunar
with one trace per leaf. Also included in his survey were several
genera from the Old World. Split-lateral traces were observed
in six species of caulescent Streptocarpus and in a few species
each of Saintpaulia,Chirita and Cyrtandra, but not in any of
100µm
vb
200µm
vb
C50µm
st
ssc
100µm
pa
lvb
ab
g
sp
se2
se1
ad
100µm
stt
g
ad
pa
sp
ab
A
DE
B
Fig. 4. Leaf structure. Streptocarpus papangae: (A) transverse section of leaf adaxial epidermis with convex epidermal cells, and sclereid (arrowhead) in the hypo-
dermis; (D) transverse section of the midrib with vascular bundles, and scattered sclereids (some indicated with arrows); (E) cleared lamina segment, astrosclereids in
the spongy mesophyll (arrows). Streptocarpus suffruticosus: (B) leaf transverse section, enlarged upper and lower epidermal cells, and stomatal turrets; (C) magnified
stomatal turret showing a ring-like arrangement of the subsidiary cells and large sub-stomatal chamber. ab abaxial epidermis, ad adaxial epidermis, g short
trichome with single celled stalk and two-celled head, lvb lateral vascular bundle with smaller branches, pa palisade layer, se1 and se2 hypodermis layers 1
and 2, sp spongy parenchyma, ssc sub-stomatal chamber, st stoma, stt stomatal turrets, vb vascular bundle.
51K. Jong et al. / South African Journal of Botany 80 (2012) 4456
the 10 species of Aeschynanthus nor in Boea hygroscopica F.
Muell. where the nodes were single traced and unilacunar.
In Streptocarpus, split-lateral traces were first recorded by
Jong (1970) for the herbaceous caulescent S. nobilis of West
Tropical Africa. In this species and in the two woody species
examined here, the lateral trace or traces originate from lower
down the internode. Most commonly as a single trace splitting
into two at the node, and in some nodes, two parallel indepen-
dent traces each journeying separately to the relevant leaf. Such
variation has also been observed by Wiehler (1983) e.g. in the
New World Columnea repens (Hook.) Hanst.
It is clear that split-lateral traces occur in both Old World
and New World Gesneriaceae. In Streptocarpus, they are pre-
sent in the woody as well as non-woody caulescent species of
both Madagascar and mainland Africa. Without further investi-
gation of the extent of their occurrence in the family, it is too
early to judge their possible taxonomic and biogeographical impor-
tance. From their scattered presence in several unrelated angiosperm
families (e.g. Chloranthaceae, Rhizophoraceae, Zygophyllaceae,
Gentianaceae, Adoxaceae, Gesneriaceae) Wiehler (1983) concluded
that this nodal type arose many times independently in the
dicotyledons.
100µm 100µm
100µm100µm
100µm 10µm
100µm
100µm
200µm
aa
fi
fi
o
sty
200µm
a
a
fi
fi
o
sty
g
A
C
E
G
I
B
D
F
H
J
Fig. 5. Leaf and floral morphology SEM images. Streptocarpus papangae: (A) adaxial epidermal surface view with convex epidermal cells and short trichomes with
multicellular heads in depressions; (C) abaxial epidermis with anisocytic stomata and groups of short trichomes with multicellular heads in depressions; (E) magnified
view of C; (G) ovary, stamens and staminodes (arrows); (I) clefted papillate stigma. Streptocarpus suffruticosus: (B) adaxial epidermal surface view with glandular
and eglandular trichomes with conspicuous multicellular foot; (D) abaxial epidermal surface view with glandular and eglandular trichomes and stomatal turrets of
varying size; (F) higher magnification of D; (H) ovary with short glandular trichomes, stamens with toothed filament (white arrow), only one staminode visible in
the figure (black arrow); (J) clefted papillate stigma. a anther, fi filament, g short trichome with single celled stalk and two-celled head, o ovary,
sty style.
52 K. Jong et al. / South African Journal of Botany 80 (2012) 4456
4.6. Sclereids
Sclereids have long been known to have a taxonomic
value in many plant groups as exemplified in Memecylon L.
(Melastomataceae) (Rao, 1957) and palms (Tomlinson, 1959).
They are rare in the family Gesneriaceae, previously recorded
for only a few genera, including Hemiboea C.B.Clarke (Wang
et al., 1998), Loxocarpus R.Br. (Sahasrabudhe, 1970)and
Aeschynanthus (Rosser and Burtt, 1969). One of the most exten-
sive surveys of foliar sclereids in the family is that on Cyrtandra
(Bokhari and Burtt, 1970; Burtt and Bokhari, 1973). In contrast to
the great diversity of sclereids reported for Cyrtandra, only a few
sclereid types have so far been observed in Streptocarpus.The
presence of sclereids in this genus was first mentioned by
Hilliard and Burtt (1971), referred to as osteosclereids (columnar
with enlarged ends, according to Dickison, 2000) in the leaf hy-
podermis of S. papangae and in another shrubby Madagascan en-
demic, S. glabrifolius. In addition, they also reported the presence
of astrosclereids (radiately branched) in the spongy mesophyll of
the latter species. The present study confirms the presence of
sclereids in both the species examined here, but their distribution
is very different from each other (Table 1). In S. papangae,their
somewhat elongated shape (wider in the middle) with even wall
thickness are more appropriately classed as macrosclereids,
which according to the terminology in Dickison (2000) are some-
what elongated with uneven secondary walls. Bokhari and Burtt
(1970) adopted a rather broader concept of osteosclereids which
included columnar to squat shaped forms. Our observations are
therefore not contradictory.
It is worth noting that exceptionally large sclereids (with
strong circular thickenings)were observed by Sahasrabudhe
(1970) in the leaf midrib of the African Linnaeopsis subscandens
B.L.Burtt. On the basis of the molecular data of Möller and Cronk
(2001a,b), species of this genus have been recently transferred to
Streptocarpus (Darbyshire, 2006). They are phylogenetically
unrelated to the woody Madagascan shrubs (Möller and Cronk,
2001a,b), and the existence of such sclereids in the Madagascan
and African species is probably the result of convergent evolution.
Sahasrabudhe (1970) also reported that all Streptocarpus
species [examined] show sclereids with circular to horse-shoe-
shaped thickenings randomly scattered in the pith and cortex
of the older stems or some cells may show depositions of lignin
at the corners. The shape of these cells scarcely differs from
those of the surrounding parenchyma cells. Sclereids of the
type here described for the Madagascan species are so far un-
known among African mainland Streptocarpus. It would be
of great interest to discover whether or not sclereid occurrence
and type are associated with growth form and geographical dis-
tribution of Streptocarpus.
4.7. Non-cohering anthers
One of the unusual features of the two woody species exam-
ined here is their possession of non-cohering anthers each at-
tached to short and stocky filaments (Fig. 5G, H). Besides S.
suffruticosus,Hilliard and Burtt (1971) observed the presence
of such anthers in several other Madagascan shrubs, namely
S. coursii and S. campanulatus. They also noted that very
100µm
20µm
m
s
f
s
100µm
fi
20µm
m
s
f
20µm
ABC
DE
Fig. 6. Stamen, ovary and ovules. Streptocarpus papangae: (A) transverse section of the mature anther with confluent sporangia; (B) transverse section of the ovary
showing ovules on recurved placenta; (C) hemi-anatropous ovule with short funicle (arrow); (D) whole mount ovule with starch pattern after Melzer staining (starch
grains stained blue-black), note funicle damaged during preparation. Streptocarpus suffruticosus: (E) ovule with curved apex, ovular starch pattern after Melzer
staining, note funicle damaged during preparation. f funicle, fi filament, m micropylar end, s starch grains.
53K. Jong et al. / South African Journal of Botany 80 (2012) 4456
short filaments occur near the base of the corolla tube in the
herb or subshrubS. macropodus and the woody shrub S.
glabrifolius, respectively 1.5 mm and ca. 1 mm long, as in S.
papangae and S. suffruticosus. It is not known whether S.
glabrifolius and S. macropodus also have non-coherent anthers.
Short filaments need not necessarily lead to non-coherent anthers,
as for example in the herbaceous caulescent Streptocarpus levis
B.L.Burtt of Madagascar, where the filaments are ca. 1.5 mm in
length, and the anthers are coherent. It remains to be determined,
however, whether non-cohering anthers are characteristic of all
the Madagascan woody species, a feature not known elsewhere
in Streptocarpus. If this turns out to be the case, it would be a
taxonomically useful synapomorphy for this species group.
4.8. Ovule morphology
The ovule in both S. papangae and S. suffruticosus is of the
hemi-anatropous type (Fig. 6C). Published information for sever-
al genera of the Gesneriaceae, as for example Rhynchoglossum
Blume and Klugia Schltdl. (subsequently subsumed into
Rhynchoglossum,Burtt, 1962) indicates that the ovule is of
the anatropous type, which had been considered typical for
the whole family (e.g. Batygina, 2006; Davis, 1966; Weber,
2004).TheoccurrenceofanotherovuletypeinStreptocarpus
was first illustrated by Anders (1966), and described in the
unpublished work of Sahasrabudhe (1970). The current study
demonstrates the presence of hemi-anatropous ovules also in
the woody Streptocarpus. A broad survey (unpublished) of
ovular morphology in the genus and across the family thus far
confirms the presence of hemi-anatropous ovules in the N20
Streptocarpus species examined, suggesting that this may well
be characteristic for the entire genus. This ovular feature would
be another notable character whose possible taxonomic signifi-
cance has hitherto been overlooked.
It may be concluded that the woody S. papangae and S. suffru-
ticosus differ from each other in certain anatomicalmorphological
features, such as trichome and sclereid distribution, stomata
structure and hypodermis, but they also possess a unique set of
characters that unite them (i.e. woodiness, non-cohering anthers,
macrosclereids) each readily differentiating them from herbaceous
caulescent Streptocarpus. They also possess relatively large seeds,
0.9 to 1.2 mm (Hilliard and Burtt, 1971; M. Möller, pers. observ.),
compared to non-woody species, 0.3 to 0.7 mm (Beaufort-
Murphy, 1983; M. Möller, pers. observ.). They also differ cytolog-
ically in their basic chromosome number, x =16, from other caules-
cent members of the subgenus Streptocarpella with x = 15.
Furthermore, we demonstrated that they possess hemi-anatropous
ovules and split-lateral leaf traces, although these are also found
in Streptocarpus of the African mainland.
The sample of woody Madagascan species investigated is too
small to deduce that the prominent woody habit, non-cohering
anthers, macrosclereids and large seeds are the only features
that characterise Hilliard and Burtt's group (iii) of Madagascan
shrubby Streptocarpus (Hilliard and Burtt, 1971). Our work
points to the necessity for further studies not only on this group
but also on other species of Madagascar and the Comoro Islands
where our knowledge is still scant. This account is but a first
fascinating glimpse of what remains to be discovered, and points
to the importance for future work to include herbaceous species
of Streptocarpus that molecular results indicate as possible allies
of the woody species.
Acknowledgements
The valuable living collection of Gesneriaceae at the Royal
Botanic Garden Edinburgh (RBGE) has facilitated this study,
thanks largely to the effective horticultural care provided by
its staff, especially S. Barber and A. Ensoll. It is a pleasure
too to acknowledge with thanks the funding MM received for
the collecting expeditions to Madagascar from The Carnegie
Trust for the Universities of Scotland, The University of
Edinburgh Davis Expedition Fund, Percy Sladen Memorial
Fund, Edinburgh Botanic Garden (Sibbald) Trust and the Royal
Botanic Garden Expedition Committee. Also much appreciated
with gratitude is the encouragement of the RBGE and the provi-
sion of excellent laboratory facilities that enabled the senior
author KJ (Honorary Associate) to pursue continuing research
in that family in close collaboration with the co-authors. Much
thanks also for the helpful comments from Louis Ronse De-
Craene that greatly improved the manuscript. We are also deeply
grateful to the late Mr. B. L. Burtt for his expansion of our knowl-
edge of the Streptocarpus of Madagascar, recognising 17 new
endemic species in addition to the 20 already known through the
pioneering work of the late Professor H. Humbert. This study is
a commemorative tribute to Bill (as he was known among friends
and colleagues) for his prodigious contribution to and profound
knowledge of the systematics of the Gesneriaceae. We would
like to thank two anonymous reviewers for their constructive
and helpful comments on an earlier version of the manuscript.
The RBGE is funded by the Rural and Environment Science
and Analytical Services division (RESAS) in the Scottish
Government.
Appendix A
Notes on cultivation of S. papangae and S. suffruticosus.
S. papangae
The specimens growing at Edinburgh are 1.4 m tall and
multi-stemmed. They are kept at a minimum night temperature
of 12 °C and have a minimum day temperature of 17 °C.
Humidity varies depending on the time of year but rarely falls
below 65% relative humidity. Day length also varies during
the year from 6.5 h in mid winter to 18 h at the height of sum-
mer; the plants are also shaded during this time to prevent
scorching. Supplementary lighting is used in part of the glass-
houses during the winter months but this can lead to soft,
weak growth and direct lighting is best avoided. Flowering usu-
ally occurs around June/July and can last for 2 months. Further
flowering can also occur in late autumn if sunny and warm. S.
papangae is grown in plastic pots, the deeper the better, using
a peat free, bark based compost. This mix provides an open,
light and free draining medium. Nutrients are added by
54 K. Jong et al. / South African Journal of Botany 80 (2012) 4456
incorporating a small amount of nine month Osmocote to pro-
vide an initial boost and thereafter liquid feeding on a weekly
or fortnightly basis with a 1:1:1 fertilizer (underfeeding rather
than overfeeding). The plants are re-potted on a bi-annual
basis or sooner if required. The only pest problem to date
has been mealy bug which can be very damaging if left
untreated.
S. suffruticosus
S. suffruticosus is grown alongside S. papangae and the con-
ditions it requires are basically similar, the main difference is
the compost and how the plants are grown. The species is gen-
erally known to be an epiphyte and therefore requires very open
compost, bark based, and a free draining pot or pond basket for
it to grow in. These plants are never very tall and usually droop
and hang down over their container. Flowering can occur sev-
eral times in a year with spring and autumn being the main pe-
riod. Feeding and re-potting is the same as in S. papangae, but
being slower growing it may not need re-potting as often. There
have been few if any pest problems with S. suffruticosus, only
the occasional mealy bug attack. It is a brave insect who gets
too close to this plant as the whole plant is covered in sticky
glandular trichomes and any insect that comes into contact
with it will have a short life.
Propagation
In principle, the same propagation methods and techniques
can be used for both species. S. papangae plants were intro-
duced to the RBGE's living collection from wild collections
in Madagascar in 1997. In the field cuttings were taken, kept
as cool as possible and wrapped in moist tissue to prevent dry-
ing out. At RBGE cuttings can be taken any time of the year but
late spring is usually best when they have just started to grow.
The cuttings should be from semi-ripe stems and about 10 cm
long, all but the top leaves are removed; the remaining leaves
may also need reducing to prevent water loss. The cuttings
are placed in medium grade perlite in small pots and watered
in well. No rooting hormone treatment is required. The propa-
gation cases should provide high humidity and bottom heat,
set to a temperature of 25 °C. New roots will start to appear
after a week or so. Supplementary lighting is also beneficial
and will speed up the rooting process.
Plants of S. suffruticosus were raised from seeds collected in
Madagascar in 1998. At RBGE we use a simple method of ster-
ilised compost in a small pot which is then placed inside a re-
sealable plastic bag; this can then be placed at 25 °C. Compost
used for sowing is a fine bark grade, with added charcoal which
is put into a 7 or 8 cm pot with boiling water put through it. The
pot is allowed to cool over night and is ready for seed sowing
the next morning. Seed is evenly scattered over the surface
and the pot labelled. There is no need to cover the seed as it
is small (ca. 0.7 mm) and light will aid germination. The reason
for the plastic bag is to prevent the pot from drying out and
from pests getting to the seed before and after germination.
Once the seeds have germinated they are fertilised weekly
with a dilute solution of a high potash fertiliser (i.e. tomato
plant food). The pot should never become too wet.
References
Anders, O., 1966. Entwicklung und Bau des Embryosacks von Streptocarpus
rexii. Flora Abteilung B, Band 156, 446451.
Batygina, T.B., 2006. Embryology of Flowering Plants. : Terminology and
Concepts, vol. 2. Seed Science Publishers Inc, Plymouth.
Beaufort-Murphy, H.T., 1983. The seed surface morphology of the Gesneriaceae
utilizing the scanning electron microscope and a new system for diagnosing
seed morphology. Selbyana 6, 220422.
Bokhari, M.H., Burtt, B.L., 1970. Studies in the Gesneriaceae of the Old World
XXXII. Foliar Sclereids in Cyrtandra: Notes from the Royal Botanic
Garden Edinburgh, 30, pp. 1121.
Burtt, B.L., 1962. Studies in the Gesneriaceae of the Old World XXIII.
Rhynchoglossum and Klugia. Notes from the Royal Botanic Garden Edinburgh
24, 167171.
Burtt, B.L., Bokhari, M.H., 1973. Studies in the Gesneriaceae of the Old World
XXXVI. Foliar sclereids in New Guinea and Pacific Cyrtandra. Notes from
the Royal Botanic Garden Edinburgh 32, 397402.
Crane, P.R., 1985. Phylogenetic analysis of seed plants and the origin of angio-
sperms. Annals of the Missouri Botanical Garden 72, 716793.
Cutler, D.F., Botha, T., Stevenson, D.W., 2007. Plant Anatomy: a Practical Ap-
proach. Blackwell Publishing Ltd, Oxford, p. 302.
Darbyshire, I., 2006. Gesneriaceae. In: Beentje, H.J., Ghazanfar, S.A. (Eds.), Flora
of Tropical East Africa. Royal Botanic Gardens Kew, London, pp. 176.
Davis, G.L., 1966. Systematic Embryology of the Angiosperms. John Wiley
and Sons Inc, New York, p. 528.
Dean, H.L., 1940. Delafield's hematoxylin and safranin for staining plant mate-
rials. Biotechnic & Histochemistry 15, 6165.
Dickison, W.C., 1980. Diverse nodal anatomy of the Cunoniaceae. American
Journal of Botany 67, 975981.
Dickison, W.C., 2000. Integrative Plant Anatomy. Harcourt Academic Press,
California, San Diego, p. 533.
Herat, R.M., Theobald, W.L., 1979. Comparative studies of vegetative anatomy
and morphology of the Gesneriaceae of Sri Lanka. Biological Journal of the
Linnean Society 78, 285298.
Hilliard, O.M., Burtt, B.L., 1971. Streptocarpus: an African Plant Study. Uni-
versity of Natal Press, Pietermaritzburg, p. 410.
Howard, R.A., 1970. Some observations on the nodes of woody plants with
special reference to the problem of the split-lateralversus the common
gap. In: Robson, N.K.B., Cutler, D.F., Gregory, M. (Eds.), New Research
in Plant Anatomy: Botanical Journal of the Linnean Society, 63, Suppl. 1,
pp. 195214.
Humbert, H., 1955. Une merveille de la nature a Madagascar: Mémoires de
l'Institute Scientifique de Madagascar, Série B. vi.
Humbert, H., 1967. Espèces nouvelles de Streptocarpus (Gesneriaceae) à
Madagascar: Adansonia, Series, 2, pp. 275294. vii.
Humbert, H., 1971. Gesnèriaceès, fam. 180. In: Leroy, J.F. (Ed.), Flore de
Madagascar. Museum National d'Histoire Naturelle, Paris, pp. 47163.
Johansen, D.A., 1940. Plant Microtechnique. McGraw-Hill Book Co, New
York, p. 523.
Jong, K., 1970. Developmental aspects of vegetative morphology of Streptocarpus.
PhD Thesis, University of Edinburgh, Edinburgh.
Jong, K., 1973. Streptocarpus (Gesneriaceae) and the phyllomorph concept.
Acta Botanica Neerlandica 22, 244245.
Jong, K., 1978. Phyllomorphic organisation in rosulate Streptocarpus. Notes
from the Royal Botanic Garden Edinburgh 36, 369396.
Jong, K., Burtt, B.L., 1975. Theevolution of morphological noveltyexemplified in
the growth patterns of some Gesneriaceae. The New Phytologist75, 297311.
Jong, K., Möller, M., 2000. New chromosome counts in Streptocarpus
(Gesneriaceae) from Madagascar and the Comoro Islands and their
taxonomic significance. Plant Systematics and Evolution 224, 173182.
MacMaster, G., Möller, M., Hughes, M., Edwards, T.E., Bellstedt, D.U., 2005.
A new species of Streptocarpus (Gesneriaceae) endemic to Madagascar.
Adansonia 27, 131136.
55K. Jong et al. / South African Journal of Botany 80 (2012) 4456
Metcalf, C.R., Chalk, L., 1950. Gesneriaceae. In: Metcalf, C.R., Chalk, L.
(Eds.), Anatomy of the Dicotyledons, Vol. 2. Clarendon Press, Oxford,
pp. 9951002.
Möller, M., Cronk, Q.C.B., 1997. Origin and relationships of Saintpaulia
(Gesneriaceae) based on ribosomal DNA internal spacer (ITS) sequences.
American Journal of Botany 84, 956965.
Möller, M., Cronk, Q.C.B., 2001a. Evolution of morphological novelty: a
phylogenetic analysis of growth patterns in Streptocarpus (Gesneriaceae).
Evolution 55, 918929.
Möller, M., Cronk, Q.C.B., 2001b. Phylogenetic studies in Streptocarpus
(Gesneriaceae): reconstruction of biogeographic history and distribution
patterns. Systematics and Geography of Plants 71, 545555.
Möller, M., Kiehn, M., 2004. A synopsis of cytological studies in Gesneriaceae.
Edinburgh Journal of Botany 60, 425447.
Möller, M., Pfosser, M., Jang, C.G., Mayer, V., Clark, A., Hollingsworth, M.L.,
Barfuss, M.H.J., Wang, Y.Z., Kiehn, M., Weber, A., 2009. A preliminary
phylogeny of the didymocarpoid Gesneriaceaebased on three molecular
data sets: incongruence with available tribal classifications. American
Journal of Botany 96, 9891010.
Puff, C., 1978. The nodal anatomy of Myrothamnus flabellifolius (Myrothamnaceae):
another example of a split-lateralcondition. Journal of the Arnold Arboretum,
Harvard University 59, 192196.
Rao, T.A., 1957. Comparative morphology and ontogeny of foliar sclereids in
seed plants. I Memecylon L. Phytomorphology 7, 306330.
Rosser, E.M., Burtt, B.L., 1969. Studies in the Gesneriaceae of the Old World
XXX. Anatomical characters in the tribe Trichosporeae. Notes from the
Royal Botanic Garden Edinburgh 29, 3958.
Sahasrabudhe, A., 1970. Phylogenetic studies in the Gesneriaceae. Anatomical
investigations into the relationships of certain genera of the tribe Didymocarpeae.
PhD Thesis, Victoria University of Manchester.
Sahasrabudhe, A., Stace, C.A., 1974. Developmental and structural variation in
the trichomes and stomata of some Gesneriaceae. New Botanist 1, 4662.
Schenk, W., 1942. Morphologisch-anatomische Untersuchungen an der
Gattung Streptocarpus Lindl. Botanisches Archiv 44, 217284.
Skog, L.E., 1976. A study of the tribe Gesnerieae, with a revision of Gesneria
(Gesneriaceae: Gesnerioideae). Smithsonian Contributions to Botany 29,
1182.
Smith, J.F., Kresge, M.E., Möller,M., Cronk, Q.C.B., 1998. A cladistic analysisof
ndhF sequences from representative species of Saintpaulia and Streptocarpus
sections Streptocarpus and Streptocarpella (Gesneriaceae) . Edinburgh Journal
of Botany 55, 111.
Solereder, H., 1908. Systematic anatomy of the dicotyledons. Translated by
Boodle, L.A., Fritsch, F.E. Vol. 1 and 2, Clarendon Press, Oxford.
Stace, C.A., 1965. Cuticular studies as an aid to plant taxonomy. Bulletin of the
British Museum, Botany 4, 178.
Tomlinson, B., 1959. Structure and distribution of sclereids in the leaves of
palms. The New Phytologist 58, 253266.
Wakefield, E.M., Dennis, R.W.G., 1950. Common British Fungi. Gawthorn,
London, p. 290.
Wang, W.T., Pan, K.Y., Li, Z.Y., Weitzman, A.L., Skog, L.E., 1998. Gesneria-
ceae. In: Wang, W.T. (Ed.), Flora of China. Science Press, Beijing, pp.
244401.
Weber, A., 2004. Gesneriaceae. In: Kubitzki, K. (Ed.), The families and genera
of vascular plants. Vol. 7. Kadereit, J.W. (vol. Ed.), Dicotyledons. Lamiales
(except Acanthaceae incl. Avicenniaceae). Springer, Berlin/Heidelberg, pp.
63158.
Weber, A., Middleton, D.J., Forrest, A., Kiew, R., Lim, C.L., Rafidah, A.R.,
Sontag, S., Triboun, P., Wei, Y.G., Yao, T.L., Möller, M., 2011. Molecular
systematics and remodelling of Chirita and associated genera (Gesneriaceae).
Taxon 60, 767790.
Wiehler, H., 1983. A synopsis of the neotropical Gesneriaceae. Selbyana 6,
1219.
Edited by AR Magee
56 K. Jong et al. / South African Journal of Botany 80 (2012) 4456
... In their monograph, Hilliard & Burtt (1971) pointed out that many Madagascan species were insufficiently known, and that groups of species exist which cannot be easily assigned to either of the two subgenera: (i) herbaceous species with leaves in a basal rosette with long petioles, sharply marked off from the orbicular blades, unbranched veins arising from the midrib, filaments fused to about a third of the corolla tube; (ii) herbaceous species with leaves in a basal rosette (rarely solitary), often attenuate at the base (petiole ill-defined), veins ascending from the base and branched, filaments fused to about a third of the corolla tube; and (iii) species of shrubby-woody habit, unbranched veins arising from the midrib, characterized also by short filaments arising at the base of the corolla. The presence of sclereids and non-coherent anthers can be added as further synapomorphies for the last group of shrubby Streptocarpus species (Hilliard & Burtt, 1971;Jong & al., 2012). The shrubby species share the basic chromosome number of x = 16 (Jong & Möller, 2000;Möller & Kiehn, 2004) and form a clade with acaulescent species (Möller & Cronk, 2001a, b;Möller & al., 2009. ...
... -Geographical and morphological data were taken from living plants cultivated in the research collection at the Royal Botanic Garden Edinburgh (RBGE), herbarium specimens at E, and consultation of the relevant literature, primarily Hilliard & Burtt (1971) for Streptocarpus, and for other genera as cited hereafter in the relevant sections. Living material was either fixed in Farmer's Fluid to aid clearing (Jong & al., 2012), or directly observed under a dissecting microscope. Some material used came from the RBGE spirit collection and was preserved in Copenhagen mix. ...
... Notes Description. -Woody shrubs with decussate leaves, axillary inflorescences, small pouch flowers, short filaments arising at the base of the corolla with non-coherent anthers, seeds long and pointed at both ends and distinctly larger (0.9-1.2 mm) than in other species (0.3-0.7 mm; Jong & al., 2012). Distributed in Madagascar. ...
Article
The taxonomy of the African, Madagascan and Comoro Island (Afro-Malagasy) Gesneriaceae attracts a large amount of interest given the horticultural importance of Cape Primroses (Streptocarpus) and African Violets (Saintpaulia). Earlier studies indicated that the Afro-Malagasy genera form a strongly supported clade, and recent classifications have included some of the genera within an expanded Streptocarpus. Given the global importance of this group, we carried out a comprehensive molecular phylogenetic analysis of all Afro-Malagasy genera in subfamily Didymocarpoideae, tribe Trichosporeae, subtribe Streptocarpinae, to investigate species relationships in these genera as the basis for a new classification. Phylogenetic analyses of the nuclear ribosomal spacer (ITS, 5S NTS) and chloroplast intron and spacer regions (rpl20-rps12 spacer, trnL intron, trnLF spacer) of 226 samples were performed, including all Streptocarpinae genera, except the monotypic Nodonema. The molecular phylogenies demonstrate that the genera with non-twisted fruits are nested within Streptocarpus which has twisted fruits. Two main clades were found, one comprising herbaceous caulescent Streptocarpus that also included Saintpaulia, the caulescents Hovanella and Schizoboea, and the unifoliates Acanthonema and Trachystigma. The second clade comprises the woody caulescents and acaulescent Streptocarpus, Colpogyne and Linnaeopsis. Altogether, twelve well-supported subclades can be recognized, each with a combination of distinct morphological characteristics. A new classification of tribe Streptocarpinae, de facto Streptocarpus, is presented, retaining the two subgenera, Streptocarpus and Streptocarpella, and dividing them into five and seven sections respectively. Nodonema is attributed to subg. Streptocarpus for morphological reasons. The former genus Saintpaulia is classified as Streptocarpus subg. Streptocarpella sect. Saintpaulia with ten species recognized.
... In common with many other gesneriad genera, Streptocarpus leaves have stomata only on the abaxial surface, with non-glandular and glandular trichomes typical of the family (Saharsrabudhe and Stace, 1974;Noel and Van Staden, 1975;Yuen and Dehgan, 1982;Jong et al., 2012). Trichomes, especially, are apparent in most publications describing morphological features of cotyledons of S.papangae and S.suffruticosus (Jong et al., 2012), of phyllomorphs and flowers (Saharsrabudhe and Stace, 1974;Viemont and Astie, 1974;Viemont, 1980) of S.rexii (Mantegazza et al., 2007;Nishii and Nagata, 2007;Nishii et al., 2012b) and of S.wendlandii (Nishii et al., 2004(Nishii et al., , 2012a. ...
... In common with many other gesneriad genera, Streptocarpus leaves have stomata only on the abaxial surface, with non-glandular and glandular trichomes typical of the family (Saharsrabudhe and Stace, 1974;Noel and Van Staden, 1975;Yuen and Dehgan, 1982;Jong et al., 2012). Trichomes, especially, are apparent in most publications describing morphological features of cotyledons of S.papangae and S.suffruticosus (Jong et al., 2012), of phyllomorphs and flowers (Saharsrabudhe and Stace, 1974;Viemont and Astie, 1974;Viemont, 1980) of S.rexii (Mantegazza et al., 2007;Nishii and Nagata, 2007;Nishii et al., 2012b) and of S.wendlandii (Nishii et al., 2004(Nishii et al., , 2012a. In various Streptocarpus species, three types of trichomes have been recognised and using the terminology of Nishii et al. (2004) they are: glandular trichomes with a unicellular glandular head and multicellular stalk (type 1), clavate glandular trichomes with a multicellular head and unicellular stalk (type 2)and needle-shaped covering trichomes (type 3). ...
Article
Full-text available
Streptocarpus dunnii Hook.f. (Gesneriaceae) grows wild in South Africa in rocky terrain and at high altitude. It possesses unique patterns of growth, is acaulescent, unifoliate and monocarpic and produces unique naphthoquinones. Morphological examinations of Streptocarpus species have tended to concentrate on germination, cotyledon anatomy and development of the primary leaf (phyllomorph) while mature phyllomorphs are rarely examined. This study sought to examine the morphology of the mature phyllomorph and to more accurately determine the type and site of naphthoquinone(s)excretion. Plants were developed from invitro plantlets originating from authenticated seeds and allowed to grow in a peat-based potting compost for a year, under ambient room conditions. Mature lamina samples were examined morphologically by light, stereo and scanning electron microscopy. Results showed anisocytic stomata only on the abaxial epidermis, with numerous non-glandular and glandular trichomes on both epidermises, especially at the proximal end of the phyllomorph. Energy-dispersiveX-ray analysis indicated both trichome types to be rich in potassium. Glandular trichomes were more abundant on the abaxial surface, especially at non-glandular trichome bases over veins and adjacent to stomata in lamina areas between veins. These trichomes were shown for the first time to be the source of the naphthoquinones in S.dunnii. Chromatographic and FT-IR analyses confirmed the glandular secretions as being mainly (±)-dunnione. Results suggest that mature phyllomorphs with densely packed epidermal trichomes and a restricted distribution of stomata are adaptations by this plant to dehydration stress, while dunnione-type naphthoquinones may function in the amelioration of oxidative stress whether of biotic or abiotic origin.
... The two members of sect. Lignostreptocarpus included here, S. papangae and S. suffruticosus, had distinctly small pollen (Figs. 2, 3;Jong et al., 2012). Other members of this section, such as Streptocarpus glabrifolius, Streptocarpus macropodus and Streptocarpus tsaratananensis also have similarly small pollen (Weigend and Edwards, 1996), a characteristic that appears to be section specific for these woody caulescent Madagascan species that also differ in their non-coherent anthers from other species in the genus where the two anthers cohere at the tip (Hilliard and Burtt, 1971). ...
Article
Full-text available
Genome size can affect the phenotype of plants by a simple physical effect of the DNA material at the cellular level. Pollen contains the bare necessities to initiate and sustain pollen tube growth and carries the haploid genome. This work investigates the extent to which the nuclear DNA content affects pollen size in an evolutionary context within Streptocarpus (Gesneriaceae), by correlating genome size with pollen size of 38 samples representing 36 taxa in a phylogenetic framework. Streptocarpus was found to possess an average genome size among diploid species of 0.82 pg (1C). Significant genome downsizing of up to 44.4% was observed among the polyploid species which are exclusively found in Madagascar. The pollen size ranged between 11.27 μm and 25.55 μm at the diploid level, but 1C values were not found to drive pollen size. On the other hand, 1C values in most polyploids showed a strong positive correlation with pollen size, near linear in species of sect. Parasaintpaulia. In a phylogenetic context, polyploidy has evolved at least twice in the genus, and contrary to pollen size, genome size was strongly lineage-specific rather than adaptive in Streptocarpus. Repeated parallel increases and decreases in genome size (1C, and 1Cx) during the evolution of the genus were inferred. Overall, in Streptocarpus at least, pollen size is a limited predictor of genome size and only partly reflecting ploidy level, but may be of taxonomic value. The study demonstrates that the relationship between pollen size and genome size is not straightforward, and their evolutionary trajectories unlinked.
Article
A new species of Streptocarpus (S. lanatus MacMaster) is described from central Madagascar. Material referable to this new taxon was previously assigned to S. ibityensis Humbert, from which it can be distinguished by its densely woolly leaves, smaller corolla lobes with purple markings, and lack of staminodes. It is endemic to Mt Itremo, where it grows in the shelter of boulders and small caves. Evidence in the form of a molecular phylogeny is presented to highlight the distinctiveness of the new species from related taxa. Both S. lanatus and S. ibityensis are classified in the IUCN category "Vulnerable". © Publications Scientifiques du Muséum national d'Histoire naturelle.