Handbook of Vanilla Science and Technology

At one time, the two New Caledonian endemics described above were classified within the genus Epistephium, but that genus of ca. 20 species is now considered to be exclusively South American in distribution. Some species (e.g. Epistephium ellipticum) are diminutive, growing only a few centimeters tall, whereas others can grow to a height of nearly 2 m. They are erect herbs of the open savannas, often found in nutrient poor, white sand areas of Brazil and Venezuela, and some even scramble loosely through surrounding vegetation, although none are actual climbers. The leaves of Epistephium exhibit reticulate venation like their New Caledonian relatives, and the stunning flowers are mostly dark pink or violet. Like so many other vanilloid orchids, however, they strongly resist cultivation attempts, usually dieing after just a year or two. The fruits of these orchids are capsules that dehisce to release distinctive seeds with circular wings - highly unusual for Orchidaceae (Cameron and Chase 1998).

Winged seeds also are found in three other genera of vanilloid orchids (Pseudovanilla, Erythrorchis, and Galeola) that are closely related and native to tropical Southeast Asia, northeastern Australia, and a few Pacific islands. All three of these genera are leafless climbing vines, two of which (Erythrorchis and Galeola) completely lack chlorophyll. These non-photosynthetic genera are exclusively parasitic on fungi, a lifestyle referred to as mycoheterotrophic. The leafless genus Pseudovanilla is similar to the other two in most regards, but does eventually develop green pigment within its stems, even if it may persist in a presumably non-photosynthetic state during the juvenile stages of its lifecycle. Recent studies have shown that these orchids are the closest living relatives of Vanilla (Cameron and Molina 2006). They climb by means of aerial roots produced at each node of the stem, just like Vanilla, and their flowers are structurally similar to those of Vanilla species. However, the fruits of all three genera are dry and dehiscent at maturity, in order to release winged seeds for dispersal by air.

There are two other genera of Vanilloideae that persist as non-photosynthetic mycoheter-otrophs: Cyrtosia and Lecanorchis. Both grow as erect herbs within forested areas of Southeast Asia, and both share a number of floral features with Vanilla. For example, the fruits of Cyrtosia are fleshy and contain small, black, spherical, crustose seeds. In contrast to Vanilla, however, the fleshy fruits of Cyrtosia are typically bright red, presumably to attract birds or mammals for dispersal (Nakamura and Hamada 1978). The plants themselves are yellow, dull orange, or light brown in color, and may grow more than 1 m tall. Lecanorchis plants are more characteristically black or dark brown in color, and less than 20 cm tall. The small flowers of Lecanorchis are similar in structure to many species of Vanilla in that the labellum is fused with the column along its margins to produce a floral tube. Also like many species of Vanilla, the labellum of Lecanorchis is ornamented with characteristic bristles and hairs, but Lecanorchis fruits are dry capsules lacking odor, and containing numerous dustlike seeds with long slender appendages of unknown adaptive advantage.

14.3 ORIGINS AND AGE OF VANILLOIDEAE

A dogmatic notion has persisted among scholars that the orchid family is a relative newcomer on the evolutionary stage of flowering plants. To support this hypothesis, botanists cite the relatively low levels of genetic diversity among orchid genera and species, many of which can be hybridized easily with one another. They cite the fact that the geologically young Andes of South America and mountains of New Guinea are major centers of orchid diversity. They cite the close relationships between orchids and social bees, which are thought to have evolved much later than other insects, and they cite the fact that most orchid subtribes and genera are found in either the Old World or the New World, butrarely across oceans, suggesting that they evolved long after the separation of the continents.