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The vanilla orchids (genus Vanilla) include about 110 flowering species in the family Orchidaceae that grow as lianas (woody vines). They are native mostly to wet tropical forests world-wide, although absent in Australia. The center of their diversity is the American tropics. The best-known species, the flat-leaved vanilla (V. planifolia), from which commercial vanilla flavoring is derived is the only orchid industrially produced for food and cosmetic purposes. It is native to the Mexico and Central America and its use has been documented by Aztecs and Mayans (Rodolphe et al. 2011; Kew RBG 2013). Another species often grown commercially but not on an industrial scale is the Pompona vanilla, V. pompona (Wikipedia 2013). Flavoring is extracted from the mature, dried pods and seeds (Kew RBG 2013).
Vanillas form long thin stems up to 35 m (115 feet) in length, with short, oblong, thick, leathery dark green leaves alternating along the vine and long aerial roots growing down from each node. A number of species have leaves reduced to scales and some with leaves absent completely so the vine is thought to photosynthesize using their green climbing stems. While most Vanilla species grow in warm wet conditions, these 18 or so leafless species are adapted to dry habitats. One exception to the lianescent form is the species V. dietschiana which grows to about 35 cm high, which has been considered different genus (Dictyophyllaria) because of its different morphology (Rodolphe et al. 2011).
There may be up to 100 flowers on a single Vanilla raceme, but usually no more than 20. The flowers are large and attractive with white, green, greenish yellow or cream colors and most have a sweet scent (although not the scent of commercial vanilla, which comes from the seed). A flower blooms only for one day, after which it falls off the stalk if not pollinated. The flowers are self-fertile but most require pollinators, which are now thought to be mostly bees; in Central America large euglossine bees. Vanilla species do not produce nectar as pollination rewards, instead pollinators collect pollen, oils and flower fragrance and/or are tricked into pollinating flowers with no reward. Hand pollination is the most reliable method of fertilizing commercially grown Vanilla (Rodolphe et al. 2011).
The fruit, called a "vanilla bean" is not a true bean, but rather a capsule 10–20 cm long, which encloses millions of tiny seeds. It ripens gradually several months after flowering, eventually turning black in color and giving off a strong aroma, and the dehiscent pod pops open allowing seeds (usually coated with sticky oil) to be dispersed by mammals, birds and insects, and in some cases by wind or simply gravity (Rodolphe et al. 2011).
The larvae of some Lepidoptera species, such as the wooly bear moths Hypercompe eridanus and H. icasia use Vanilla species as food plants (Rodolphe et al. 2011).