Draba ruaxes

Perennials; (cespitose, forming tufts); caudex branched (with persistent leaf-bases, branches some terminating in sterile rosettes); scapose. Stems unbranched, 0.2–0.6 (–0.8) dm, often pubescent throughout, sometimes glabrate distally, trichomes simple, 0.4–1 mm, and 2–4-rayed, 0.1–0.4 mm. Basal leaves rosulate; subsessile; petiole base and margin ciliate, (trichomes simple, 0.4–1.4 mm); blade oblanceolate to obovate or suborbicular, 0.3–1 cm × 2–4.5 mm, margins entire, surfaces pubescent, abaxially with stalked, 2–10-rayed, stellate trichomes, 0.2–0.8 mm, adaxially with simple trichomes, 0.4–1 mm, sometimes with smaller, 2–4-rayed ones, (midvein obscure). Cauline leaves 0. Racemes (2–) 4–10 (–14) -flowered, ebracteate, elongated in fruit; rachis not flexuous, pubescent as stem or glabrous. Fruiting pedicels ascending to divaricate-ascending, straight or slightly curved upward, 3–7 (–9) mm, pubescent or glabrous, trichomes simple and 2–4-rayed. Flowers: sepals ovate, 2–3 mm, pubescent, (trichomes simple with fewer, 2-rayed ones); petals bright-yellow, obovate, 4–6 × 2–3.5 mm; anthers oblong, 0.4–0.5 mm. Fruits elliptic to lanceolate or ovate to suborbicular, plane, flattened, 4–8 (–10) × 3–4.5 mm; valves puberulent, trichomes simple with fewer 2-rayed ones, 0.1–0.35 mm; ovules 12–16 per ovary; style 0.5–0.9 (–1.1) mm. Seeds oblong, 1.5–2 × 1–1.3 mm. 2n = 72.

Phenology: Flowering Jun–Jul.
Habitat: Rock outcrops, talus slopes, ridges, alpine summits
Elevation: 500-2400 m

Alta., B.C., Yukon, Alaska, Wash.

Discussion

C. L. Hitchcock (1941) treated Draba ruaxes as a variety of D. ventosa; as demonstrated by G. A. Mulligan (1971b), the two are quite distinct. Draba ruaxes is an outcrossing hexaploid with well-formed anthers and pollen, and abundant, simple trichomes on leaves, stems, sepals, and fruits. By contrast, D. ventosa is an apomictic triploid with abortive anthers and/or pollen, and no simple trichomes anywhere on the plant.

Selected References

None.

Lower Taxa