Polystachya is a genus of approximately 230 epiphytic and lithophytic orchids in the family Orchidaceae (order Asparagales), commonly known as the yellowspike orchids. It is abbreviated Pol in the horticultural trade. The genus was formally described by the Scottish botanist William Jackson Hooker in 1824 and serves as the type genus of the subtribe Polystachyinae, a grouping within the diverse orchid tribe Vandeae.
The genus is distinguished within the orchids by its resupinate flowers — or, more precisely, by its non-resupinate flowers: unlike most orchids, Polystachya blooms are oriented so that the lip (labellum) faces upward rather than downward, giving the inflorescence a characteristic appearance. Plants are typically small to medium-sized, growing as epiphytes on tree branches or as lithophytes on rocks in humid tropical forests, and produce pseudobulbs that store water and nutrients.
Polystachya encompasses roughly 100–230 species (estimates vary by authority) distributed broadly across the tropics, with the greatest diversity in sub-Saharan Africa. Species are also found in Madagascar, South and Southeast Asia, the Pacific islands, and the Neotropics. The genus has attracted interest among orchid enthusiasts for the often fragrant, delicate flowers produced in racemes or panicles, which range in colour from white and yellow to pink and purple depending on the species. Members of the genus are grown in cultivation as ornamental plants, though they require the warm, humid conditions of their native tropical habitats.
Etymology
The genus name Polystachya comes from the Greek polys (many) and stachys (spike or ear of grain), referring to the multi-spiked or many-racemed inflorescences characteristic of plants in this group.
Distribution
Polystachya is distributed across tropical regions worldwide, with the centre of diversity in sub-Saharan Africa. Species occur from West and Central Africa through East Africa and Madagascar, extending to the Arabian Peninsula, South and Southeast Asia, the Pacific, and tropical America. The genus favours humid montane and lowland forests, growing primarily as epiphytes on trees.
Taxonomy Notes
Polystachya was described by William Jackson Hooker in 1824 and is the type genus of the subtribe Polystachyinae within Orchidaceae. GBIF recognises the genus as accepted within the order Asparagales. Species counts differ by authority: Wikipedia cites approximately 100 species; other sources recognise upwards of 200. The subtribe Polystachyinae is placed within the tribe Vandeae in most modern classifications.
Cultivation
Polystachya species are grown by orchid enthusiasts worldwide. They are generally cultivated in warm to intermediate conditions with high humidity, bright but indirect light, and good air circulation, reflecting their epiphytic lifestyle in tropical forests. Plants are often mounted on cork or bark slabs, or grown in small pots with coarse, well-draining orchid mix. They should be watered regularly during active growth and given a brief drier rest period after pseudobulb maturation.
