Draba cana |
Draba argyrea |
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Brewer's Draba, canescent Draba, canescent whitlow-mustard, cushion Draba, hoary Draba, hoary whitlow-grass, lance-leaf Draba, lance-leaf whitlow-grass |
silver Draba |
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Habit | Perennials; caudex simple or branched (branches short); not scapose. | Perennials; caudex branched (branches loose, creeping, sometimes terminating in sterile shoots); scapose. |
Stems | unbranched or branched distally, (0.6–)1–3(–3.8) dm, pubescent throughout, trichomes simple, 0.5–1mm, with 4–10-rayed ones, 0.05–0.2 mm (mostly branched on basal parts). |
unbranched, (0.2–)0.3–0.8(–1.1) dm, pubescent proximally, glabrous distally, trichomes short-stalked to subsessile, 5–8-rayed, 0.05–0.2 mm. |
Basal leaves | rosulate; petiolate; petiole ciliate throughout; blade linear to oblanceolate or oblong, (0.5–)0.8–2(–3.5) cm × 1.5–4(–11) mm, margins entire or dentate, (base and apex ciliate, trichomes simple, 0.3–0.8 mm), surfaces pubescent with short-stalked, 4–12-rayed trichomes, 0.1–0.3 mm. |
rosulate; subsessile; petiole base and margin not ciliate, (midvein obscure abaxially); blade oblanceolate to obovate, 0.3–0.7(–1.2) cm × 1–2.5(–4) mm, margins entire, surfaces canescent with short-stalked, 8–12-rayed, stellate trichomes, 0.1–0.2 mm. |
Cauline leaves | 3–10(–17), (not overlapping); sessile; blade lanceolate to ovate or oblong, margins entire or dentate, surfaces pubescent as basal (adaxially with simple and forked trichomes near blade base). |
0. |
Racemes | (10–)15–47(–63)-flowered, basally bracteate, often considerably elongated in fruit; rachis not flexuous, densely pubescent, trichomes 4–10-rayed (0.05–0.2 mm), and fewer simple ones. |
2–8(–12)-flowered, ebracteate, elongated in fruit; rachis slightly flexuous, usually glabrous, rarely sparsely pubescent as stem. |
Flowers | sepals (green or lavender), oblong to ovate, 1.5–2 mm, pubescent, (trichomes simple and few-rayed); petals white, oblanceolate to spatulate, 2.3–3.7(–4.5) × 0.7–1.7 mm; anthers ovate, 0.1–0.2 mm. |
sepals ovate, 2–3 mm, pubescent, (trichomes 4–6-rayed); petals yellow, oblanceolate, 4–6 × 1.5–3 mm; anthers ovate, 0.5–0.6 mm. |
Fruiting pedicels | suberect or ascending, straight, 2–5(–10) mm, pubescent as rachis. |
divaricate-ascending, straight or slightly curved upward, (4–)5–12(–19) mm, glabrous. |
Fruits | (subappressed to rachis), linear-lanceolate to linear or, rarely, ovate-oblong, slightly twisted or plane, flattened, (5–)6–11 × 1.5–2(–2.5) mm; valves pubescent, trichomes short-stalked, 3–7-rayed, 0.05–0.3 mm; ovules 28–48 per ovary; style 0.1–0.6 mm. |
lanceolate to elliptic or ovate, plane or slightly twisted, flattened, 5–11 × 2–3.5(–4.5) mm, (symmetric); valves often puberulent, sometimes glabrous, trichomes simple and subsessile, 2–4-rayed, 0.03–0.2 mm; ovules 8–14 per ovary; style (0.7–)1–1.8(–2.4) mm. |
Seeds | ovoid, 0.5–0.7(–0.9) × 0.3–0.5 mm. |
oblong, 1.2–1.8 × 0.8–1.1 mm. |
2n | = 32. |
= 36. |
Draba cana |
Draba argyrea |
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Phenology | Flowering (May-)Jun–Aug. | Flowering Apr–Jul. |
Habitat | Rock outcrops and talus, open prairie benchlands, roadsides, meadows, alpine tundra | Rock crevices, ledges, talus slopes |
Elevation | 0-4100 m (0-13500 ft) | 1000-3100 m (3300-10200 ft) |
Distribution |
AK; CA; CO; ID; ME; MI; MT; NH; NM; NV; SD; UT; VT; WA; WI; WY; AB; BC; MB; NB; NF; NT; ON; QC; SK; YT; Greenland
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ID |
Discussion | The limits of Draba cana have long been confused, and the species was treated as a synonym of the Himalayan D. lanceolata Royle (M. L. Fernald 1934; C. L. Hitchcock 1941) or as a variety of the western North American D. breweri (R. C. Rollins 1993). However, G. A. Mulligan (1971) clearly demonstrated that all three are distinct and should be maintained. Some Utah plants corresponding to the type of D. valida have shorter and wider oblong-ovate fruits. In all other aspects, they are indistinguishable from D. cana. Additional studies are needed to establish whether such plants should be formally recognized. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
M. A. Beilstein and M. D. Windham (2003) hypothesized that Draba argyrea is an allopolyploid derived through hybridization between D. lonchocarpa and D. sphaerocarpa. The species is restricted to Blaine, Boise, Custer, and Elmore counties in central Idaho. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Source | FNA vol. 7, p. 298. | FNA vol. 7, p. 292. |
Parent taxa | Brassicaceae > tribe Arabideae > Draba | Brassicaceae > tribe Arabideae > Draba |
Sibling taxa | ||
Synonyms | D. breweri var. cana, D. valida | D. argyrea var. glabrescens |
Name authority | Rydberg: Bull. Torrey Bot. Club 29: 241. (1902) | Rydberg: Bull. Torrey Bot. Club 30: 251. (1903) |
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