The Stained Glass Palm, Geonoma epetiolata

Abstract

Geonoma epetiolata is the only neotropical palm that exhibits substantial leaf mottling. This article provides a summary of its biology and conservation, some observations of natural populations and a discussion of the ecological role of leaf mottling.
PALMS 51: 139-146 (2007).

Full text

PALMS Blanco & Martén-Rodríguez: Geonoma Vol. 51(3) 2007
139
The Stained-
Glass Palm,
Geonoma
epetiolata
MARIO A. BLANCO
Department of Botany,
University of Florida,
220 Bartram Hall,
Gainesville, Florida 32611
USA
and
Jardín Botánico Lankester,
Universidad de Costa Rica,
Apdo. 1031-7050
Cartago, Costa Rica.
mblanco@flmnh.ufl.edu
AND
SILVANA MARTÉN-RODRÍGUEZ
Behavior, Ecology, Evolution
and Systematics (BEES),
Biology-Psychology Building
144,
University of Maryland,
College Park, Maryland
20742 USA
smartenr@umd.edu
Geonoma epetiolata is the only neotropical palm that exhibits substantial leaf
mottling. This article provides a summary of its biology and conservation, some
observations of natural populations and a discussion of the ecological role of leaf
mottling.
PALMS 51(3): 139–146
1. Geonoma epetiolata in the
forest understory, Omar Torrijos
National Park, Panama. Note
contrasting colors of the
expanding new leaf (yellow-
purple) and the most recent
mature leaf (green), both with
substantial mottling.

Palm leaves display a great morphological
diversity; however, leaf color in most species
is uniformly green. Color variation occurs in
some species, where the sheaths and petioles
are red or orange (e.g., Areca vestiaria,
Cyrtostachys renda), the adult leaves are covered
with a blush grey bloom (e.g., Brahea
decumbens, Bismarckia nobilis), the lower leaf
surface is almost completely white (Cryosophila
and Arenga spp.), or the new expanding leaves
are bright red (e.g., Actinokentia divaricata,
Welfia regia, Calyptrocalyx spp.). However,
relatively few species normally have truly
variegated leaves.
In almost all palms with naturally variegated
leaves, the variegation is expressed as mottling
(roundish dark spots on a lighter background,
or vice-versa; Dransfield 1974, Tucker 1992).
This type of leaf variegation is well exemplified
by various species of Pinanga and a few species
and varieties of Licuala, both of them Asian
and Malesian genera. But perhaps the most
vividly colored foliage among variegated palms
belongs to the Tropical American Geonoma
epetiolata, the Stained-Glass Palm.
Described less than 30 years ago (Moore 1980),
G. epetiolata remains relatively unknown
despite its attractive foliage (Fig. 1). The few
accounts of this species in the literature
mention the unusual leaf pigmentation very
briefly (Henderson et al. 1995, Ellison & Ellison
2001, Grayum 2003, Riffle & Craft 2003). The
original description mentioned only the red or
purple lower surface of the leaves (Moore
1980). Only recently has some information
about this species become available online
(Gray 2006).
Distribution and habitat
The Stained-Glass Palm occurs in a few sites in
Panama and Costa Rica. In Panama,
populations are known from the provinces of
Coclé, Colón, San Blas, and Veraguas. It is said
that the type population north of Santa Fe de
Veraguas has been extirpated by unscrupulous
collectors, but this has not been verified by
us. In Costa Rica, the Stained-Glass Palm is
restricted to a narrow band of premontane rain
forest that includes the northeastern part of
Braulio Carrillo National Park and three
adjacent private reserves. We have seen G.
epetiolata in three locations: the private reserves
Rara Avis and Terra Folia in Costa Rica, and in
Omar Torrijos National Park in Panama (Fig.
2).
All known populations of G. epetiolata occur on
the Caribbean slope of montane areas between
300–1000 meters above sea level. In Braulio
Carrillo National Park in Costa Rica, at least 37
other palm species, including eight species of
Geonoma, occur at the same elevational band
(Chazdon 1987).
Annual precipitation is very high at all the
locations where G. epetiolata occurs. In Rara
PALMS Blanco & Martén-Rodríguez: Geonoma Vol. 51(3) 2007
140
2. Caribbean slope of Cerro Calvario in Omar Torrijos National Park, Panama, one of the sites where the
Stained-glass Palm occurs.

Avis private reserve for example, annual
rainfall averages 6 to 7 meters, and a record of
over 10 meters was recorded in 1997. This
precipitation falls aseasonally throughout the
year, although there are occasional dry spells.
Even between rains the sky is almost always
overcast. Consequently, the understory is
generally very dark. The plants grow in the
understory of primary forest on poor lateritic
soils, but with abundant leaf litter on the soil
surface.
Vegetative morphology
Plants of G. epetiolata have solitary brown
stems that can (rarely) reach 2.5 meters in
height, but most plants are less than 1 meter
tall. The diameter of the stem is 1–1.5 cm.
About five to ten leaves can be present at once,
and the largest ones reach 60 cm in length. The
leaves are undivided, cuneate-oblanceolate in
shape, and are bifid to almost one-fourth of
their length (Fig. 1). Each bifurcation is acute
at the tip, but when the leaves have not
expanded completely the margins can be
folded under, which creates the false
impression of a rounded tip with an acuminate
apex. The blades taper gradually towards the
junction with the stem, where they form a
short fibrous sheath without a connecting
petiole (thus the specific epithet). The leaves
are pleated between the veins, which run at a
narrow angle relative to the midrib.
The leaves can be quite narrow, up to five times
as long as wide. The type collection (Dressler
4777) has these narrow leaves. This seems to
PALMS Blanco & Martén-Rodríguez: Geonoma Vol. 51(3) 2007
141
3. New leaves are almost
completely devoid of
chlorophyll while
expanding.

be an extreme of the variation, however, and
the leaves can be proportionately wider, up to
2.5 times as long as wide; variation in leaf
proportions has also been noticed by other
observers (see Gray 2006). When fully
expanded, young leaves appear wider than
mature ones. During preparation of herbarium
specimens the leaves seem to become
somewhat narrower, probably because the
plications become more pronounced after
drying.
The most remarkable feature of the species is
the beautiful color pattern of its foliage (Front
Cover, Figs. 1 & 3). Young leaves are pale
yellow with green veins, and marked with
prominent red purple blotches more or less
randomly over the upper surface. Frequently,
but not always, the lower surface is flushed
with red purple. The expanding leaves stand
more or less erect, and when illuminated from
behind they appear really luminous, like a
pane of stained glass (thus the common name).
Only the youngest leaf in each plant has these
bright colors. Young leaves of G. epetiolata are
similar to those of Pinanga veitchii (see back
cover of Principes 34(2), April 1990), but the
spots are red purple instead of brown.
As soon as they mature, the leaves turn into a
beautiful light emerald green, and the spots
change from purple to dark green (Fig. 1). The
texture of the upper leaf surface is not smooth
but micropapillate, which gives it an opaque,
velvety appearance. This combination of colors
and texture make the mature leaves look like
a thick pane of green sanded glass with dark
stains at the opposite side. The red color
frequently disappears from the underside of
very old leaves, or from most mature leaves in
plants exposed to bright light (Figs. 4).
Chazdon (1991) detected a correlation between
plant size and degree of leaf complexity among
species of Geonoma. Species with short stems
tend to have small, undivided leaves, while
taller species have progressively larger leaves
with more divisions. Furthermore, for species
with bifid (undivided) leaves, small leaves are
more efficient than large ones in terms of
shade tolerance (Chazdon 1986). Geonoma
epetiolata fits this pattern well, as it is one of
the smaller species in the genus. Its undivided,
epetiolate leaves form something like a funnel,
and dead vegetable matter frequently
accumulates among the leaf bases of large
individuals (Back Cover). Raich (1983) studied
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142
4. On this plant, only the youngest leaf shows the red underside. Notice three inflorescences, one with fruits.

this phenomenon in Asterogyne martiana,
another short understory palm with undivided
leaves and very short petioles; he hypothesized
the impoundment of debris is an adaptation
to increase the quantity of nutrients available
to the plant. When it rains, nutrients from the
decomposing debris leach to the base of the
stem and toward the roots.
Reproductive structures and phenology
Plants of G. epetiolata become reproductive at
approximately 10 years of age (based on the
average rate of leaf production and counts of
leaf scars in the smallest reproductive plants
seen). The unbranched inflorescences are
borne from the leaf axils, and they can persist
on the stem after the subtending leaf has
fallen. One of us studied the reproductive
biology of G. epetiolata in Costa Rica (Martén
& Quesada 2001), and found that the spikes
take from three to seven months to elongate
completely after they emerge from their
enclosing bract and prophyll. The rachis can
reach 40 cm in length, and is held more or less
erect at first (Fig. 4). Each spike starts with a
male phase, and produces one to three
staminate flowers per day for up to six months
(Fig. 5). After all staminate flowers are spent
the inflorescence enters the female phase (13
to 28 days), during which up to 25 pistillate
flowers are produced each day. This extended
flowering period per inflorescence is among
the longest recorded for any palm.
Each plant produces new inflorescences
continuously, so that spikes on male and
female stages often co-occur on the same plant.
The plants are self-compatible, and they can
be successfully fertilized with their own pollen
(Martén & Quesada 2001). However, because
staminate and pistillate flowers are present on
different inflorescences at any given moment,
even self pollination has to be mediated by a
pollinating agent.
Neither staminate nor pistillate flowers
produce any nectar, and very few insect visitors
were observed. Among these were weevils,
drosophilid flies and stingless bees; none of
them could be positively identified as a true
pollinator. From 1020 flowers marked, only
13% initiated fruit and 75% of these aborted
prematurely. Some abortions were caused by
weevil predation (Martén & Quesada 2001).
After fertilization, the ovary swells and turns
from yellow to green. The fruits ripen after
five to nine months and turn dark purple.
They are subglobose, about 0.6 cm in diameter.
No animal dispersers were observed during the
two-year phenology study, and many fruits
simply fell to the ground after an average of
54 days on the inflorescence (Martén &
Quesada 2001). This suggests that gravity is
the main form of fruit dispersal, but it is likely
that frugivorous birds also disperse some fruits.
This low seed dispersal capability might
explain why populations of G. epetiolata are
so restricted geographically.
De Nevers and Grayum (1998) found that the
populations east of El Copé (central-western
Panama) have female flowers with digitate
staminodial tubes, whereas those to the west
(including the Costa Rican one) have crenate
staminodial tubes. Both morphs co-occur in El
Copé. The degree of staminodial tube lobing
in female flowers of Geonoma is important
taxonomically, but this seems to be the only
difference among eastern and western
populations of G. epetiolata (de Nevers &
Grayum 1998).
Why the leaf colors?
The micropapillate leaf texture and the abaxial
anthocyanin layer on young leaves might
represent adaptations to maximize the capture
of photosynthetically active radiation (PAR)
in the dark forest understory. Lee et al. (1979)
demonstrated that the abaxial anthocyanin
layer present in the leaves of many tropical
understory plants reflects most of the PAR that
has traveled through the leaf uncaptured by
the photosynthetic pigments back into the
mesophyll. Geonoma epetiolata grows in
extremely low light environments, so its red
leaf undersides are adaptive in this respect.
PALMS Blanco & Martén-Rodríguez: Geonoma Vol. 51(3) 2007
143
5. Few male flowers are produced per day on each
spike.

The abaxial layer of anthocyanins might also
protect the photosynthetic pigments from the
negative effects of ultraviolet radiation during
the formation of the new leaf (Gould 2004).
However, this is unlikely to explain leaf
coloration in an understory specialist such as
G. epetiolata. An alternative explanation is that
anthocyanins protect new leaves against fungal
infections and insect herbivores (Coley &
Barone 1989, Gould 2004).
Mottled leaves, even when attractive to the
human eye, probably have the opposite desired
effect: they can serve as camouflage. Most large
mammal folivores of the forest floor (e.g., deer,
tapirs, etc.) are color blind, and the mottling
might hide the leaves from their sight by
“breaking” their outline, so they “blend” with
the background (Stone 1979, Givnish 1990,
Tucker 1992) (Fig. 6). Another possibility is
that the spots make the leaves appear diseased
or senescent. In fact, most plants with
naturally mottled foliage are short herbs of the
forest understory, where they are more
susceptible to defoliation by grazing mammal
herbivores (Givnish 1990). All species of
Pinanga with mottled leaves are understory
palms; the species with the most strikingly
mottled leaves in the genus, P. veitchii, is a very
short plant, and larger species of Pinanga that
have mottled leaves as juveniles loose some
of the mottling intensity after they grow tall.
However, several epiphytes, notably some
bromeliads, also have mottled or fenestrated
foliage. Benzing and Friedman (1981) found
that the dark spots on these bromeliads have
higher concentrations of chlorophyll and
likely have higher photosynthetic rates than
the surrounding “pale” areas of the same leaf.
They suggested that the patchy distribution of
chlorophyll on the leaf optimizes the nutrient
economy of the plant in a nutrient-poor
environment and improves the light harvest
of plants with multi-layered canopies in
exposed situations. This hypothesis is also an
unlikely explanation for the mottling in G.
epetiolata, which occurs in the dark forest
understory. Benzing and Friedman (1981) did
not explicitly consider the potential role of
leaf variegation as camouflage or disease
mimicry as a defense against herbivory.
Most palms with mottled foliage tend to turn
uniformly green when exposed to increased
light levels (Tucker 1992). This provides further
support for the understory camouflage
hypothesis, because the mottling would be
ineffective as camouflage in open areas,
although Ferrero (2006) reported that the
strongly mottled Licuala mattanensis can
PALMS Blanco & Martén-Rodríguez: Geonoma Vol. 51(3) 2007
144
6. New leaves of G. epetiolata are very attractive to the human eye because of their colors (left). The same
photograph in grayscale (right), approximates the vision of a color-blind mammal herbivore; notice how the
mottling “breaks” the outline of the leaf and makes it harder to see against the background.

tolerate full sun. The camouflage hypothesis,
therefore, still awaits rigorous experimental
testing (Allen & Knill 1991).
It is puzzling that no other neotropical
understory palms have substantial leaf
mottling (lowland populations of Chamaedorea
tuerckheimii have a subtle mottling), while this
phenomenon is more widespread among
Malesian palms. Almost all of these, however,
belong to the genus Pinanga (Dransfield 1974),
which suggests this trait evolved only a few
times among them.
Cultivation
The Stained-Glass Palm has never been
common in cultivation, and has the reputation
of being difficult to grow. A few small plants
are grown successfully at Lankester Botanical
Gardens in small pots with an organic mix
and a generous layer of mulch on top. They
should be kept under intermediate
temperatures and be watered daily. A couple of
plants are in cultivation in the Atlanta
Botanical Garden, where they are doing well
planted in a highly organic mix designed for
epiphytes. The species is reportedly in
cultivation also in the Harold L. Lyon
Arboretum (University of Hawaii at Manoa)
and in a few private collections (Gray 2006).
In order to preserve the beautiful mottling and
red undersides of the leaves, the plants should
never be exposed to bright light, as already
mentioned above. A few days of bright light
(not even direct sunlight) will cause the leaves
to turn almost uniformly green, and the
affected leaves will not revert to the normal
mottling even if the plant is returned to a
shadier place (R. Determann, personal
communication). Dransfield (1974) suggested
that a nutrient-poor substrate could increase
the intensity of the variegation in species of
Pinanga, but this does not seem to be a
requirement for G. epetiolata. Plants grow very
slowly; populations in Costa Rica produce a
new leaf approximately every six months (S.
Martén-Rodríguez, unpublished data).
Geonoma seeds have a reputation for being
difficult to germinate, and those of G. epetiolata
are no exception. Several attempts to propagate
the species in Costa Rica have consistently
resulted in disapointingly low germination,
although rigorous experiments to test the
effects of different environmental conditions
and scarification treatments have yet to be
carried out. Ellison and Ellison (2001) reported
that seeds of this species can germinate within
two to three months of planting, but gave no
details about treatment.
Conservation status
The conservation status of Geonoma epetiolata
has not been assessed before. Johnson (1996)
listed this species in his Appendix 3 (Endemic
palms with unknown conservation status) as
being restricted to Panama, although as already
said, it also occurs in Costa Rica.
At least in the two populations we have seen,
the Stained-Glass Palm is locally abundant and
protected within national parks and private
reserves. Seedlings are not uncommon and
there seems to be good recruitment. The
condition of the other Panamanian
populations is unknown to us. Habitat loss
through deforestation is always a concern,
given that there are so few known populations.
The Stained-Glass Palm is also threatened by
collection of seedlings and adult plants for the
ornamental plant trade. The owners of the
private reserves in Costa Rica where the
Stained-Glass Palm occurs are well aware of its
presence there and they look after them. Illegal
collectors have been discovered on a few
occasions. Given the slow growth rates of these
palms and their low fruit set, any decrease in
their populations can threaten the long term
survival of the species.
Chazdon (1987) recommended seed germi-
nation studies for several ornamental palms
in Costa Rica (including G. epetiolata) for
propagation purposes, as a sustainable
alternative to collection of plants from the
wild. Johnson (1996) suggested that nurseries
for propagation of ornamental palms should
preferentially be established as close as possible
to their natural populations, so the local
people can acquire an appreciation of the
palms, perceive a benefit from their presence
in nature and feel compelled to protect them.
The area of occupancy of G. epetiolata in Costa
Rica is estimated to be 50 km2(Martén &
Quesada 2001), and the known populations
in Panama probably occupy less than 150 km2
altogether, taking into account the likely loss
of habitat through deforestation. The extent of
the species as a whole is likely declining. Given
these circumstances, G. epetiolata should
probably be listed as Vulnerable according to
the IUCN Red List criteria (IUCN 2001).
Acknowledgments
We thank Ron Determann (Atlanta Botanical
Garden) for information on his experience
PALMS Blanco & Martén-Rodríguez: Geonoma Vol. 51(3) 2007
145

growing Geonoma epetiolata. Suggestions by
John Dransfield and Robin Chazdon improved
the manuscript. The Organization for Tropical
Studies provided partial funding for the
reproductive biology component of the
research in Costa Rica by S. Martén-Rodríguez.
Fieldwork in Panama and Costa Rica by M.
Blanco was made possible by a U.S. National
Science Foundation grant (DEB-0234064) to
Norris H. Williams and W. Mark Whitten
(Florida Museum of Natural History, University
of Florida) for phylogenetic studies of subtribe
Maxillariinae (Orchidaceae).
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