Orchidaceae

Habit: Plant a vine, occasionally reaching up to 10 meters. Climbs via aerial roots, short, thin, ca 0.2 X 3cm, unbranched. Terrestrial roots long, thin, superficial.

Main axis: Stems thin, brittle, ca. 0.4 – 0.7 cm in diameter, internodes 8 – 10 cm, one to many branched.

Inflorescence: Inflorescences racemose, axillary, sessile, 2 - 8 flowered, fleshy, green; bracts green, triangular, ca. 1 x 1 cm.

Flowers: Flowers not resupinate, fleshy, very stiff, distichous on raceme, ca. 7 cm wide, slightly fragrant (like cut grass or trunk slash); pedicel with ovary, pale yellow-green, straight, ca 0.3 X 3 cm (pedicel of auto-pollinating individuals may be longer because fruit development begins in bud stage); sepals green, stiff, elliptic, apex acute, margins keeled, undulated, ca 1.7 x 4 cm, petals green, stiff, strongly reflexed backwards, margins crisped or not, ca 1.2 x 4 cm, lip white, distinctly three-lobed; middle lobe 3cm long, attached to column on dorsal side for 0.4 cm of length, distinctive yellowish channel formed from two raised longitudinal ridges, undersurface with distinct longitudinal furrow; lateral lobes white, ca 1.8 cm long, stiff, forming triangular opening with middle lobe as base; callus absent; column 2.4 cm long, 0.4 mm wide, stiff, forks 0.4 cm from tip of stigma, upper fork holds anther sac curving slightly upwards continuing 0.3 cm beyond stigma; rostrellum absent; anther sac with red-orange fringe, 0.2 x 0.2 cm; stigma distinctive with four nipple-like projections, ca 0.05 x 0.2 cm.

Fruit: Fruit cylindrical, ca 1 X 18 cm, disagreeable fragrance when moist.

Distribution: This species is relatively common throughout the Amazon basin (Soto-Arenas, pers. com.). Although in our study region it occurs more abundantly in association with M. flexuosa wetlands, it is the only species not strictly restricted to wetlands. For example, we have documented individuals growing in managed banana plantations, suggesting that it is a fast-growing, colonizing species. In M. flexousa wetlands with deep histosols and acidic waters it generally prefers areas with abundant, low-lying, shrubby trees common to wetlands, such as Ilex sp. (Aquifoliaceae), Tapirira guianensis (Anacardiaceae), and Tabebuia insignis (Bignoniaceae). The leaf litter of these common, non-palm wetland trees may be important in seedling germination.

Ecology: Flowering phenology is somewhat sporadic; various individuals flowered in Jan, Apr, May, and Nov during 2005-2006. The number of flowers per individual ranged from five to about 50, depending on plant size. Flowers often open in triplets and remain open for three to seven days as observed for other membranaceous species (Soto-Arenas, Cameron et al. 2003). Due to longer flower longevity and rapid rates of anthesis a large floral display often accumulates on reproductive branches. The most gregariously flowering branches are almost always those that are pendent, hanging from the main vegetative axis.

Vanilla guianensis is apparently self-pollinated at early anthesis as the stigma and anther sac grow to contact one another. Pollination rates are approximately 78% (Table 1). No potential pollinators have been observed but Soto-Arenas (2003) suggests that the stiff flowers and relatively closed throat of V. guianensis may be adapted to large, strong pollinators such as Carpenter bees (Xylocopa spp). However, no Xylocopa species have been observed near flowers of V. guianensis in wetlands during two years of studies of their abundant populations in the region.

Unlike other Vanilla species, the flower and column of V. guianensis rapidly abscise from the developing fruit. Once mature, dehiscing fruits have a rather unpleasant, putrid odor for one week to one month before the fruit completely desiccates. While such odors may be attractive to some animal dispersers, none, however, have been observed near fruits. The thin brittle stems are not easily propagated vegetatively and seedling survival is low. For these reasons it tends to occur in much lower densities than other species.

Notes: This species has a complicated nomenclature, with no type specimen and several synonyms. The oldest name is V. guianensis Split and thus conserved. However, it may also be found as V. acuta Rolfe, V. latisegmenta Ames, and V. surinamensis Rchb.f. (Soto-Arenas, pers comm.) A member of the membranaceous clade distinguished by their thin leaves, continuous endoderm comprised of a large number of row fibers in the stem, and little differentiation between vegetative and reproductive axes.