Wall.
Description
Parnassia pusilla is a diminutive grass-of-Parnassus distributed through the central and eastern Himalaya, recorded from China, Nepal, India, Bhutan and Myanmar and represented by some 177 georeferenced occurrences. It is a plant of cold, wet, open high-elevation ground, characteristically inhabiting alpine seepages, marshy meadows, dripping rock ledges and the gravelly margins of snowmelt streams where the substrate remains saturated through summer. The specimen photographed below Dzongri in Sikkim at about 3950 m in August illustrates its strong affinity for the upper alpine flush zone, where it flowers during the brief monsoon-fed growing season among low cushion vegetation and short turf.
It is a small, glabrous perennial herb arising from a short rootstock, forming a basal rosette from which slender, single-flowered scapes emerge. The basal leaves are long-petiolate with ovate to cordate blades, while each flowering stem bears a single sessile, clasping cauline leaf below the flower. The solitary flower is regular and pentamerous, with five free white petals that are conspicuously veined. Characteristic of the genus, alternating with the fertile stamens are five fringed staminodes, each dissected into gland-tipped filaments that serve as pseudonectaries to attract pollinators. The superior ovary develops into a capsule that splits to release numerous small seeds.
Despite its placement here under Celastraceae, Parnassia is morphologically distinctive, and the family circumscription reflects modern molecular treatments that subsume the former Parnassiaceae within an enlarged Celastraceae. The elaborate gland-tipped staminodes are a notable adaptation for insect pollination, offering visual and possibly olfactory rewards without true nectar. As a specialist of high-altitude wetlands, P. pusilla is sensitive to drainage, trampling by livestock and the desiccation of alpine seeps, so it serves as a useful indicator of intact high-mountain mire habitat.
Author: Wall. · Sources: POWO (Kew), GBIF, Flora of China Vol. 8, Flora of Bhutan Vol. 1, Flora of Nepal, Wu Phylogeny and Biogeography of the Genus Parnassia