Draba caesia Adams

Perennials; (cespitose, usually forming mats); caudex branched (covered with persistent leaf bases); usually scapose. Stems unbranched, 0.2-0.8(-1.2) dm, pubescent throughout, trichomes minutely stalked, 8-15-rayed, stellate, (non-crisped), 0.03-0.15 mm. Basal leaves rosulate; petiole (obsolete), ciliate throughout; blade oblanceolate to obovate, 0.2-0.9(-1.5) cm × 1-3(-5) mm, margins entire, (not ciliate), surfaces usually pubescent, rarely glabrescent, with short-stalked, 8-15-rayed, stellate, (non-crisped) trichomes, 0.05-0.15 mm. Cauline leaves 0 or 1; sessile; blade ovate or oblong, margins entire, surfaces pubescent as basal. Racemes 3-9(-11)- flowered, ebracteate, elongated in fruit; rachis often slightly flexuous, pubescent as stem. Fruiting pedicels usually ascending, rarely divaricate, straight, 1-4.5(-8) mm, pubescent as stem. Flowers: sepals ovate, 1.5-2 mm, pubescent, (trichomes simple and short-stalked, 2-5-rayed); petals white, spatulate to oblanceolate, 2-3.5 × 0.8-1.4 mm; anthers ovate, 0.2-0.3 mm. Fruits elliptic to narrowly oblong-elliptic, twisted or not, flattened, 3.5-9 × 1.5-2.2 mm; valves usually glabrous, rarely with 3-6-rayed trichomes on replum; ovules 12-24(-28) per ovary; style 0.1-0.4 mm. Seeds ovoid, 0.6-1 × 0.5-0.6 mm. 2n = 16.

Flowering Jun-Aug. Rock outcrops and fellfields, meadows, open tundra, stream banks, gravelly beaches, roadsides; 0-2500 m; Greenland; Alta., B.C., Man., Nfld. and Labr. (Nfld.), N.W.T., Nunavut, Ont., Que., Yukon; Alaska; Europe (Finland, Norway [including Svalbard], n, w Sweden); e Asia (Russian Far East, n Siberia); Atlantic Islands (Iceland); circumpolar.

Draba nivalis is most often confused with D. lonchocarpa, and C. L. Hitchcock (1941) reduced the latter to a variety (var. elongata) of D. nivalis. A critical comparison reveals that there are enough differences to warrant their recognition as distinct species. Draba nivalis is distinguished by having non-ciliate leaf bases, basal leaf blades pubescent with trichomes 0.05-0.15 mm, stems and pedicels that are always pubescent, and fruits that are elliptic to narrowly elliptic-oblong, plane, and 3.5-9 mm. By contrast, D. lonchocarpa has ciliate leaf bases, basal leaf blades pubescent with trichomes 0.15-0.5 mm, stems and pedicels that are glabrous or sparsely pubescent, and fruits that are linear to lanceolate or oblong, slightly twisted or plane, and 6-15(-18) mm. Except for Alaska, D. nivalis does not grow in the continental United States, whereas D. lonchocarpa grows in nearly all Mountain and Pacific states.