Plants (0.5-)1-8(-20) cm. Stems often reddish, branched or simple, rooting adventitiously from proximal nodes. Leaves: ocrea brownish, broadly funnelform, 1-1.5 mm, margins oblique; petiole (0.1-)2-10 mm; blade 1-6.5 × 1-5 mm, base tapering to truncate, apex obtuse to acute, glabrous. Pedicels 0.1-1.5 mm or absent. Flowers: perianth 0.9-1.8 mm; tepals ovate to elliptic, margins entire, apex obtuse; stamens ca. 1/ 2 as long as tepals. Achenes 1-1.8 × 0.7-0.8 mm, dull. 2n = 14 (Mongolia, Norway), 28.
Flowering Jul-Aug, fruiting Aug-Sep. Arctic tundra and alpine meadows with permanently moist gravel, especially around persistent snow patches near streams, ponds, and lakes; 0-4400 m; Greenland; Alta., B.C., Man., Nfld. and Labr. (Labr.), N.W.T., Nunavut, Ont., Que., Yukon; Alaska, Colo., Mont., Utah, Wyo.; s South America (Argentina, Chile); n Europe; c, e Asia.
Koenigia islandica is among the smallest of terrestrial flowering plants and one of few annual species in arctic and alpine floras. Some other species exhibit a similar bipolar distribution (e.g., Anemone multifida Poiret, Osmorhiza chilensis Hooker & Arnott, and Carex macloviana D'Urville).