Mart.
2100m April
Description
Arisaema costatum is a tuberous aroid of the central and eastern Himalaya, recorded by GBIF from Nepal, China, India and Bhutan across about 99 occurrences. It is a herb of moist, shaded broadleaved and mixed forest, forest margins, ravines and damp humus-rich slopes at mid montane elevations. The photographed plants come from Nepal at Honngaon (2300 m, May), eastern Nepal in the Mewa-Khola (2100 m, April) and the Helambu at Samathang (2410 m, May), a consistent band of cool, humid forest understorey where this cobra-lily emerges with the spring rains.
The plant arises from a depressed globose tuber and typically produces a single large pedate leaf divided into numerous lanceolate, acuminate leaflets, the central one largest, the lamina conspicuously ribbed, the costae giving rise to the epithet costatum. The inflorescence is a spadix enveloped by a spathe whose tube is greenish and the limb dark purple to maroon, strongly striped with white, and drawn out into a long, slender, pendent filiform tail. Arisaema species are commonly paradioecious, individuals shifting sex with size and vigour: smaller plants bear staminate flowers, larger ones pistillate. Pollinated by fungus-gnats lured into the spathe, fertile plants ripen a dense club of bright red berries.
GBIF accepts the name. The genus Arisaema is a centre of Himalayan diversity, with A. costatum among its most striking species for the boldly white-striped, long-tailed spathe. The size-dependent sex change is an adaptive reproductive strategy linked to tuber resources. Widespread within suitable forest, the species is not regarded as threatened, though forest clearance locally reduces its habitat.
Author: Mart. · Sources: POWO (Kew), GBIF, Flora of Nepal, Flora of China, Gusman monograph of Arisaema