Wall. ex Meisn.
Description
Polygonum filicaule is a small Himalayan and East Asian knotweed ranging from the Himalaya through southern China to Taiwan and Japan; GBIF lists around 358 occurrences across China, India, Pakistan, Japan and Taiwan. It inhabits cool, moist temperate sites, growing in damp turf, moss carpets, stream banks, marshy meadows and seepage zones, often as a prostrate component of open subalpine grassland. The accompanying photograph from Phobjika in Bhutan at about 2800 m in early June shows the species at the start of its flowering season in the broad, marshy glacial valley floors for which that locality is well known. Under POWO this name is treated as a synonym, the accepted name being Persicaria filicaulis.
It is a delicate, creeping, mat-forming perennial herb with thread-like (filiform), much-branched stems that root at the lower nodes, the epithet filicaule alluding to these slender stems. The ochreae are membranous, tubular and shortly ciliate, sheathing the nodes. Leaves are small, ovate to oblong-lanceolate, shortly petiolate or subsessile, with entire margins and often a fine pubescence. Flowers are minute and few, borne in short, lax terminal or axillary clusters; the perianth is five-parted, white to pink, persistent and enclosing the fruit. The achene is small, trigonous, dark brown and lustrous.
The species belongs to a group of diminutive, mat-forming Asian polygonums now widely placed in Persicaria, distinguished from robust upright knotweeds by their creeping habit and reduced inflorescences. As a wetland and seepage specialist it contributes to high-altitude turf communities and is well adapted to grazed, trampled and seasonally waterlogged ground. It is not considered threatened, being widespread and tolerant of disturbance, though dependent on the persistence of moist montane grassland.
Author: Wall. ex Meisn. · Sources: POWO (Kew), GBIF, Flora of Bhutan, Flora of China (Polygonaceae), Hara & Williams Enumeration of the Flowering Plants of Nepal