Apostasia, commonly known as grass orchids, is a genus of about eight species of primitive terrestrial orchids belonging to the family Orchidaceae (order Asparagales). Unlike the vast majority of orchids, members of Apostasia are barely recognisable as such: they are evergreen, grass-like plants with scaly rhizomes, thin stems bearing many long narrow leaves arranged spirally, and small yellow or white star-shaped flowers borne on short, often branched flowering stems.
The flowers of Apostasia depart markedly from the typical orchid blueprint. In most orchids one petal is modified into a distinctive labellum and the dorsal sepal differs from the lateral sepals; in Apostasia all three sepals and three petals are similar in size, shape, and colour. The column is also unusual in possessing three separate stamens (rather than the two found in most orchids), and the pollen grains are free rather than massed into pollinia — features that place the genus firmly in the subfamily Apostasioideae alongside its only relative, Neuwiedia.
Phylogenetic studies indicate that Apostasia and Neuwiedia, despite their apparently "primitive" traits, are sister genera rather than direct ancestors of the rest of the orchid family. The genus was first formally described in 1825 by the Dutch botanist Carl Ludwig Blume, published in Bijdragen tot de flora van Nederlandsch Indië. Representative species include Apostasia wallichii and Apostasia fujianica.
Etymology
The genus name Apostasia derives from the Ancient Greek word apostasis, meaning "defection" or "departure from." The name alludes to the many features that distinguish this genus from typical orchids — including its free stamens, non-consolidated pollen, and uniformly similar floral parts.
Distribution
Apostasia species occur in humid tropical and subtropical forests from north-eastern India, Nepal, and Bhutan east to southern Japan, and south through Southeast Asia (including the Himalayan foothills, China, Sri Lanka, and Indochina) to New Guinea and northern Australia (Queensland). Three species are recorded from China, one of which is endemic, and one species is endemic to Queensland.
Taxonomy Notes
Apostasia is placed in the subfamily Apostasioideae of the family Orchidaceae, where it sits alongside the monotypic genus Neuwiedia. Together these two genera are distinctive within Orchidaceae in bearing three (rather than two) stamens that are free from the style, and in producing loose pollen rather than compact pollinia. Although these features were once interpreted as ancestral ("primitive") within the family, molecular phylogenetic studies now support Apostasioideae as the sister group to all remaining orchids rather than as a grade of primitive precursors. The genus was established by Carl Ludwig Blume in 1825.
