(DC.) H.Ohashi & R.R.Mill
Description
Hylodesmum laxum is a widely distributed forest herb of warm-temperate and subtropical Asia, recorded from Japan, China, Taiwan, the Philippines, Indonesia, Papua New Guinea, India, Vietnam, Sri Lanka, Thailand, Nepal and Bhutan, with some 740 georeferenced occurrences. It is a characteristic understorey element of moist broad-leaved and mixed evergreen forests, favouring shaded slopes, forest margins and streamside thickets on humus-rich soils. In the eastern Himalaya it ascends to the middle montane belt, as illustrated by the material gathered near Wangdi in central Bhutan at about 2700 m in September, when it flowers and fruits in the post-monsoon season.
The species is a perennial herb with erect or ascending, slender, ridged stems arising from a woody rootstock. The leaves are pinnately trifoliolate and crowded toward the stem apex, the terminal leaflet rhombic-ovate to elliptic and larger than the lateral ones, acuminate and entire, thinly membranous and sparsely appressed-pubescent. The inflorescence is a lax, elongate terminal raceme or panicle bearing small papilionaceous flowers with a pink to pale purple corolla, the standard obovate and the keel obtuse. The fruit is a flattened, stipitate loment constricted between the segments, the articles covered with uncinate hairs that promote epizoochorous dispersal.
The genus Hylodesmum was segregated from Desmodium by Ohashi and Mill to accommodate species with stipitate, deeply constricted loments and a forest-herb habit, and H. laxum is among its more widespread members. Its very broad transcontinental range, spanning the Himalaya to the western Pacific, points to effective long-distance dispersal by the hooked fruit articles. Locally common and of no immediate conservation concern, its populations nonetheless remain dependent on intact forest cover, and the species is a useful indicator of relatively undisturbed montane woodland.
Author: (DC.) H.Ohashi & R.R.Mill · Sources: POWO (Kew), GBIF, Flora of China Vol. 10, Flora of Bhutan Vol. 1, Flora of Nepal, Ohashi & Mill revision of Hylodesmum (Desmodium group)