(Hook.f.) Soó
Description
Platanthera leptocaulon is a terrestrial orchid of the eastern Himalaya and adjacent mountains of south-western China, recorded from Sikkim and the rest of northern India, Nepal, Bhutan, Myanmar and Yunnan and Sichuan in China. The roughly 67 georeferenced collections concentrate in the high subalpine to alpine belt, where the species occupies moist open turf, the margins of dwarf-shrub thickets and grassy hollows kept damp by snowmelt. The plant photographed above Chora in Sikkim at 3600 m in August typifies its habitat, flowering during the late-summer monsoon at elevations of roughly 3000-4200 m on humus-rich, well-drained slopes.
It is a slender, glabrous herb arising from ovoid to fusiform root-tubers, the erect stem comparatively thin and wiry (the epithet leptocaulon meaning "slender-stemmed"). The few cauline leaves are oblong-lanceolate to linear, sheathing at the base and grading upwards into bracts. The lax terminal raceme bears small greenish to greenish-white flowers; the dorsal sepal and petals are connivent to form a hood over the column, the lateral sepals spreading, and the entire, narrowly oblong labellum extends backwards into a slender cylindrical spur. The viscidia are naked and the pollinia are attached by slender caudicles, with fruit a small erect dehiscent capsule releasing dust-like seed.
The genus Platanthera is a large Holarctic and Asian assemblage centred on temperate and montane regions, and P. leptocaulon belongs to the species-rich Sino-Himalayan radiation, the basionym having been transferred by Soo from Habenaria. Like most members of the genus it depends on mycorrhizal fungi for germination and probably on long-tongued nocturnal pollinators attracted to the spurred flowers. Though not formally assessed, its broad transboundary range and tolerance of grazed alpine pasture suggest reasonable security, but populations remain vulnerable to overgrazing and the warming-driven upslope contraction of alpine grassland.
Author: (Hook.f.) Soó · Sources: POWO (Kew), GBIF, Flora of China, Flora of Bhutan, The Genus Platanthera (Orchidaceae) monograph