Cryptostylis

Cryptostylis, commonly known as tongue orchids, is a genus of terrestrial orchids belonging to the Orchidaceae family. These plants are found across a broad geographical range, extending from South Asia and Southeast Asia through to Australia and New Zealand, as well as islands in the South Pacific.

Description and Morphology

Plants in the genus Cryptostylis are perennial herbs that grow terrestrially, characterized by a thick, branching underground rhizome from which vertical shoots emerge. They possess thick, fleshy roots but do not form tubers. Each year, new leaves are produced, typically numbering one to a few, arising from the base of the flowering stem. These leaves have a distinct petiole and are often purplish on their lower surface. However, some species, such as C. hunteriana, are saprophytic and leafless.

The inflorescence is a raceme bearing one to a few non-resupinate flowers. The sepals and petals, excluding the labellum, are narrow and similar in appearance to each other. The most striking feature of the flower is the labellum, which is attached to the base of the column and closely encircles it. Following pollination, the fruit develops as a thin-walled capsule containing a large number of seeds.

Taxonomy and Naming

Cryptostylis was first formally described by the botanist Robert Brown in 1810. The genus name is derived from the Ancient Greek words 'kryptos' (hidden) and 'stylos' (pillar or column), a reference to the column of the orchid being partially concealed by the labellum. Molecular studies of the DNA of tongue orchids indicate that the genus belongs to the tribe Diurideae within the orchid family, having previously been placed in the Cranichideae. Cryptostylis and the New Caledonian endemic genus Coilochilus together form the subtribe Cryptostylidinae.

Distribution and Habitat

The genus comprises approximately twenty-five species, distributed from India, Sri Lanka, Thailand, Taiwan, the Philippines, and Malaysia, extending through Indonesia to Australia and New Zealand. The distribution also includes Samoa, New Caledonia, and Vanuatu. Five species are found in Australia, with three of these being endemic to the continent. Tongue orchids inhabit a range of environments, from temperate to tropical regions, and can be found in sites with well-drained soil as well as swampy areas. Cryptostylis arachnites has the widest distribution within the genus and typically grows in rainforests, often in mountainous terrain.

Ecology and Pollination

All Australian species of Cryptostylis are pollinated by the ichneumon wasp, Lissopimpla excelsa, often referred to as the orchid dupe wasp. This pollination occurs through a phenomenon known as pseudocopulation, where male wasps attempt to mate with the flowers, mistaking them for female wasps. This remarkable strategy was first documented by Australian naturalist Edith Coleman in 1928. While mimicry of female insect parts by flowers has been observed in other orchid genera, Cryptostylis is unique in that the observed insect has been documented ejecting seminal fluid containing sperm cells. It is suggested that male wasps are more strongly attracted to the orchid flowers than to actual female wasps of the same species. Color perception studies indicate that the flowers and female wasps share similar colors when viewed under the visual system of hymenopterans, despite appearing different to human eyes. The visual spectrum of wasps includes green, blue, and ultraviolet wavelengths. Unusually for insect-pollinated orchids, several Cryptostylis species are pollinated by the same wasp species, whereas many other orchids that mimic insects are highly species-specific in their pollinators. Although undetectable to humans, the flowers emit an odor that attracts the orchid dupe wasp, and gas chromatography has identified specific compounds responsible for this attraction across different Cryptostylis species.