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FNA | Family List | FNA Vol. 7 | Brassicaceae | Draba

32. Draba cusickii B. L. Robinson ex O. E. Schulz in H. G. A. Engler, Pflanzenr. 89[IV,105]: 105. 1927.

Draba sphaeroides Payson var. cusickii (B. L. Robinson ex O. E. Schulz) C. L. Hitchcock

Perennials; (loosely cespitose); caudex branched (with few, persistent leaf remains); scapose. Stems unbranched, 0.3-1.2 dm, pubescent throughout, tri-chomes (2-)4-rayed, 0.05-0.5 (-0.6) mm. Basal leaves rosulate; shortly petiolate; petiole base ciliate (margin not ciliate, trichomes 2-rayed, 0.3-0.6 mm); blade oblanceolate to obovate, 0.4-1.2 cm × 2-5 mm, margins entire or, rarely, denticulate, surfaces pubescent with stalked, (2-)4-rayed trichomes, 0.15-0.4 mm. Cauline leaves 0. Racemes 10-20(-25)-flowered, ebracteate, considerably elongated in fruit; rachis not flexuous, pubescent as stems proximally. Fruiting pedicels divaricate-ascending, straight (not expanded basally), 4-9 mm, pubescent, trichomes (2-)4-rayed, (0.05-0.25 mm). Flowers: sepals broadly ovate, 2-2.5 mm, pubescent, (trichomes short-stalked, 3- or 4-rayed); petals yellow, obovate to oblanceolate, 3.7-6 × 1.5-2.5 mm; anthers ovate, 0.5-0.6 mm. Fruits lanceolate to broadly ovate, plane, flattened, 6-9 × 2-4.5 mm; valves pubescent, trichomes short-stalked, (2-)4-rayed, 0.05-0.25 mm; ovules 10-18 per ovary; style 0.4 0.8(-1) mm. Seeds oblong, 1.2-1.5 × 0.7-0.8 mm. 2n = 26.

Flowering Jun-Jul. Basaltic outcrops, talus, rocky soil; 2000-2700 m; Oreg.

Draba cusickii was divided by R. C. Rollins (1993) into two varieties with significantly different morphologies and chromosome numbers. The Nevada endemic var. pedicellata (2n = 20) is here treated as a distinct species following M. D. Windham (2004). Draba cusickii has the same chromosome number as D. sobolifera but is readily distinguished from that species by having 4-rayed (versus simple or 2-rayed) fruit trichomes. Draba cusickii is known from Steens Mountain (Harney County).


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