Orchidaceae

Habit: Plant a vining epiphytic herb in crowns of M. flexuosa. Attaches to host via aerial roots produced from each node, thin, unbranched, 3 – 100 cm in length, tannish in color.

Main axis: Stems green, thin, somewhat fleshy, ca. 0.4 cm in diameter, internodes 8.5 – 10.5 cm long.

Leaves: Leaves alternate, produced from each node opposite to roots, ca. 2.5 X 5.1 cm – 4.5 X 11cm, drooping from long petioles; petiole u-shaped in cross-section, ca. 1cm in length, red to purple; leaf blade elliptic, apex acute, margin entire with red to purple outline, texture smooth.

Inflorescence: Inflorescences racemose, axillary and terminal, fleshy, green, sessile, one to 20 per individual, ca 1 to 10-flowered, non-floriferous bracts generally two; bracts red to purple ca 0.3 x 0.6cm.

Flowers: Flowers resupinate, fleshy, tender, 10cm across, arranged spirally on raceme, non-fragrant; pedicel with ovary, dark red when young, maturing to green, ca. 3 cm long and 0.2 cm in diameter; buds deep red; dorsal sepal orange, elliptic-oblanceolate, ca. 0.7 x 7.5 cm; lateral sepals orange, elliptic-oblanceolate, 0.9 x 7.5 cm; petals orange-red, oblanceolate-linear, ca. 0.6 x 6.5cm; lip trumpet-like in shape, flabellate and almost triangular when flattened, fused with column for three quarters of its length, exterior ringed white around mouth fading to yellowish-orange, soft and yellow tomentom of papillose hairs form distinct patch connecting callus to opening; callus diffuse, 0.7 x 0.3 cm; column straight, 4.2 cm long, 0.2 cm wide, ventral surface hirsute for about a third of its length, then glabrous; rostrellum thin, narrow, white; anther sac 0.3 x 0.4 cm.

Fruit: Fruit cylindrical, ca. 10 cm long, non-fragrant, quick-drying.

Distribution: This species has a wide distribution, previously being collected in Ecuador, British Guyana, and Venezuela. This is the first documentation of V. bicolor in Peru, significantly extending its range to the south. It is a common epiphyte of (or rarely found growing on) M. flexuosa. Long, slender roots reach deep into the slender pocket formed between the sheathing petiole bases of palm fronds and the trunk. In our region it is largely restricted to M. flexuosa wetland habitat characterized by deep histosols and acidic waters. Within this specific habitat type, the species is occasionally encountered as a short terrestrial vine in very open areas with high insolation. These uncommon individuals reach maximum heights of 3 to 4m well below canopy level and never reach epiphytic status in M. flexousa crowns. Terrestrially rooted individuals likely result from the clonal propagation of fallen epiphytes rather than seedling germination and represent the exception, rather than the rule, thus we maintain its classification as a true epiphyte. It often occurs with V. pompona.

Ecology: The flowers of V. bicolor are non-fragrant, open singly at approximately five-day intervals, and last for a period of less than one day. Flowering phenology is fairly aseasonal. We have observed flowers during all 12 months of the year, although there seems to be a slight peak in August during the height of the dry season.

Pollination rates are extremely high, falling between the ranges of 45% to 75% (Table 1). No local pollinators have been observed at or near flowers and bagging experiments suggest that the plant is self-pollinating. Self-pollination seems to be achieved by the secretion of excess stigmatic fluids that creates a mixture of moisture and pollen grains. The rather thin, narrow rostrellum is an ineffective barrier between the pollen-fluid mixture and the stigmatic surface, greatly facilitating self-pollination through excessive stigmatic leak.
Fruiting phenology is aseasonal. Mature fruits, which are quick-drying and non-oily, can be observed throughout the year. The mechanism of seed dispersal of V. bicolor is unknown. Lack of fragrance, oils, or sugars, presence of extremely small seeds, and its canopy habitat are all suggestive of dispersal by a mixture between wind turbulence and gravity. As the fruits dehisce and dry, the seeds are exposed to strong winds and then fall downward. Seedlings are abundant, germinating almost exclusively in the small openings between palm trunks and the sheathing petiole bases of palm fronds. This species is not easily propagated vegetatively.

Notes: Possibly synonymous with V. wrightii Rchb. F (Soto-Arenas, pers. comm.). It is a primitive member of the American clade of fragrant Vanilla (Soto-Arenas, Cameron et al. 2003). This, and sister species V. palmerum (below), differ from all other American Vanilla (except for the Membranaceous group [V. guianensis]), in that the penicillate callus is not compact, but rather diffuse.