Draba petrophila |
Draba argyrea |
|
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Santa Rita Mountain Draba, Santa Rita Mountain whitlowgrass, Santa Rita whitlow grass |
silver Draba |
|
Habit | Perennials; (cespitose, long-lived); caudex simple or branched (covered with persistent petioles), not scapose. | Perennials; caudex branched (branches loose, creeping, sometimes terminating in sterile shoots); scapose. |
Stems | usually unbranched, rarely branched, 0.3–1.9(–2.8) dm, moderately to densely hirsute throughout, trichomes simple, 0.2–1.3 mm, with short-stalked to subsessile, cruciform, 0.02–0.4 mm, and 2-rayed ones, 0.3–0.9 mm. |
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, (trichomes simple, 0.4–1.5 mm); blade oblanceolate, 1–5(–6) cm × 2–5(–10) mm, margins usually entire, rarely denticulate, surfaces pubescent, abaxially with stalked, cruciform trichomes, 0.07–0.5 mm, adaxially often similar, sometimes with fewer, simple and 2-rayed trichomes, 0.4–1.3 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; sessile; blade ovate to lanceolate or oblong, margins entire or denticulate, surfaces pubescent as basal. |
0. |
Racemes | 10–37(–58)-flowered, ebracteate, elongated in fruit; rachis not flexuous, pubescent as stem. |
2–8(–12)-flowered, ebracteate, elongated in fruit; rachis slightly flexuous, usually glabrous, rarely sparsely pubescent as stem. |
Flowers | sepals oblong, 2–3.5 mm, pubescent, (trichomes simple and 2-rayed); petals yellow, oblanceolate, 3.5–6 × 1.2–1.8 mm; anthers oblong, 0.8–1 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 | divaricate-ascending, straight, 4–10 mm, pubescent throughout, trichomes simple (0.1–0.5 mm) and subsessile, 2–4-rayed, (0.03–0.2 mm). |
divaricate-ascending, straight or slightly curved upward, (4–)5–12(–19) mm, glabrous. |
Fruits | lanceolate to elliptic, often strongly twisted, flattened, 5–11 × 2–3 mm; valves puberulent at least along margin, trichomes simple, antrorse, 0.03–0.15 mm; ovules 14–24 per ovary; style 0.8–1.8(–2.5) 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, 1–1.4 × 0.6–0.9 mm. |
oblong, 1.2–1.8 × 0.8–1.1 mm. |
2n | = 36. |
|
Draba petrophila |
Draba argyrea |
|
Phenology | Flowering Jul–Sep. | Flowering Apr–Jul. |
Habitat | Crevices, ledges of cliffs | Rock crevices, ledges, talus slopes |
Elevation | 1200-2800 m (3900-9200 ft) | 1000-3100 m (3300-10200 ft) |
Distribution |
AZ
|
ID |
Discussion | Draba petrophila is often broadly circumscribed to include the taxon herein called D. viridis. For a discussion of the differences between these species and the closely related D. helleriana, see I. A. Al-Shehbaz and M. D. Windham (2007). Draba petrophila, in the strict sense, is known only from Cochise, Pima, and Santa Cruz counties in southeastern Arizona. (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. 329. | FNA vol. 7, p. 292. |
Parent taxa | Brassicaceae > tribe Arabideae > Draba | Brassicaceae > tribe Arabideae > Draba |
Sibling taxa | ||
Synonyms | D. helleriana var. blumeri, D. helleriana var. petrophila | D. argyrea var. glabrescens |
Name authority | Greene: Pittonia 4: 17. (1899) | Rydberg: Bull. Torrey Bot. Club 30: 251. (1903) |
Web links |