Bistorta perpusilla (Hook.f.) Greene, Leafl. Bot. Observ. Crit. 1: 21 1905. (Syn: Polygonum perpusillum Hook. f.);
East Himalaya, Nepal, West Himalaya as per POWO;
Common name: Tiny Knotweed

Polygonaceae Fortnight polygonum perpusillum from Rohtang Pass ,Kullu Dist, HP : 3 posts by 3 authors. Attachments (1).
Shot from Rohtang zero Point at 4000m

A very good finding …! Big thanks for sharing this typical alpine Himalayan element!!
Better to call it Bistorta perpusilla (Hook. f.) Greene 



Bistorta perpusilla (Hook.f.) Greene (Polygonaceae) photographed above Bhagwabasa, Roopkund area (Chamoli) Uttarakhand. Second image is a cropped up part of first.
2600m altitude.