Draba densifolia |
Draba serpentina |
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dense-leaf Draba, dense-leaf whitlow-grass, Nuttall's Draba, Nuttall's whitlow-grass |
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Habit | Perennials; (cespitose, pulvinate); caudex branched (dense with persistent leaf remains, branches sometimes terminating in sterile rosettes); scapose. | Perennials; (cespitose); caudex branched (with persistent leaves, branches sometimes terminating in sterile rosettes); scapose. |
Stems | unbranched, (0.05–)0.2–1(–1.7) dm, usually glabrous, rarely pubescent, trichomes usually simple, 0.3–0.8 mm, and 2–4 (or 5)-rayed, 0.1–0.6 mm, (rarely predominantly simple ones). |
unbranched, 0.3–1.3 dm, glabrous throughout. |
Basal leaves | rosulate; sessile; blade linear to oblong or oblanceolate-linear, 0.3–0.9(–1.4) cm × 0.5–1.5(–2) mm, margins entire, (ciliate, trichomes simple, 0.3–1.2 mm), surfaces glabrous or sparsely pubescent, abaxially with short-stalked, 2–4-rayed trichomes, 0.1–0.3 mm (midvein prominent), adaxially rarely with subapical, simple trichomes. |
rosulate; sessile; blade obovate to obovate-oblanceolate, 0.4–1 cm × (2–)2.5–4(–5) mm, margins entire, (ciliate, trichomes simple, 0.2–0.5 mm, apex acute), surfaces glabrous. |
Cauline leaves | 0. |
0. |
Racemes | 2–10(–22)-flowered, ebracteate, not or slightly elongated in fruit; rachis not or slightly flexuous, glabrous or pubescent as stem. |
6–14-flowered, ebracteate, elongated in fruit; rachis not flexuous, glabrous. |
Flowers | sepals ovate, 2–3 mm, usually sparsely pubescent, rarely glabrous, (trichomes simple and short-stalked, 2–4-rayed); petals pale yellow (sometimes fading white), oblanceolate to obovate, 2–5 × 1–1.7(–2) mm; anthers ovate or oblong, 0.4–0.6 mm. |
sepals ovate, 2–3 mm, glabrous; petals white, spatulate to obovate, 5–6.5 × 2–3 mm; anthers ovate to oblong, 0.4–0.5 mm. |
Fruiting pedicels | divaricate-ascending to ascending (not decurrent basally), straight, (0.7–)1.5–10(–25) mm, usually glabrous, rarely sparsely pubescent, trichomes predominantly simple (0.2–0.7 mm), sometimes 2–4 (or 5)-rayed, (0.1–0.5 mm). |
divaricate-ascending, straight, 5–13 mm, glabrous. |
Fruits | ovoid or ovate-lanceolate, plane (not curved), flattened, (2.5–)3–6(–8) × 2–3 mm; valves pubescent or puberulent, trichomes simple and short-stalked, 2–5-rayed, 0.1–0.4 mm; ovules 4–12 per ovary; style 0.3–0.6(–1) mm. |
lanceolate to narrowly oblong, slightly twisted or plane, flattened, 6–12 × 2–3.5 mm; valves glabrous; ovules 8–16 per ovary; style 0.6–1.8(–2.5) mm. |
Seeds | oblong to ovoid, 1.2–2(–2.6) × 0.9–1.2(–1.4) mm. |
oblong, 1.1–1.4 × 0.7–0.8 mm. |
2n | = 36. |
= 52. |
Draba densifolia |
Draba serpentina |
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Phenology | Flowering Jun–Aug. | Flowering May–Jul. |
Habitat | Rock outcrops and talus, rocky knolls, alpine ridges | Rock outcrops, talus, and gravelly soil in mixed conifer and subalpine meadow communities |
Elevation | 800-3700 m (2600-12100 ft) | 3200-3600 m (10500-11800 ft) |
Distribution |
AK; CA; ID; NV; OR; UT; WA; WY; AB; BC
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NV |
Discussion | Draba densifolia is one of the most highly variable North American members of the genus, as evidenced by the extensive synonymy. The species is an apomict (G. A. Mulligan 1976) and it occupies tremendous geographic, edaphic, and altitudinal ranges. In forms corresponding to the type of D. sphaerula, the flowering stems are 2-flowered, and the stems, leaves, and fruiting pedicels are to 5, 1.5, and 0.6 mm, respectively. By contrast, forms comparable to the type of D. caeruleomontana var. piperi have stems, leaves, and fruiting pedicels to 17, 1.3, and 2.5 cm, respectively. Between these remarkable extremes fall all of the other populations of the species. Draba densifolia is sometimes confused with D. paysonii, which it resembles, in being a cespitose, scapose, and densely pulvinate perennial having narrowly linear or oblong to linear-oblanceolate leaf blades with strongly ciliate margins. It is easily distinguished from the latter by having glabrous adaxial leaf blade surfaces, only sparsely pubescent abaxial surfaces, and often glabrous fruiting pedicels and rachises. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Of conservation concern. Draba serpentina has been treated by other authors as a variety or synonym of D. oreibata. As indicated by I. A. Al-Shehbaz and M. D. Windham (2007), the two taxa are morphologically distinct, have different chromosome numbers, and are separated by over 480 kilometers. They are treated herein as separate species. Draba serpentina is known only from the Snake Range (White Pine County) and the Toiyabe Mountains (Lander County) in central Nevada. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Source | FNA vol. 7, p. 306. | FNA vol. 7, p. 335. |
Parent taxa | Brassicaceae > tribe Arabideae > Draba | Brassicaceae > tribe Arabideae > Draba |
Sibling taxa | ||
Synonyms | D. caeruleomontana, D. caeruleomontana var. piperi, D. glacialis var. pectinata, D. globosa var. sphaerula, D. mulfordiae, D. nelsonii, D. oligosperma var. pectinata, D. pectinata, D. sphaerula | D. oreibata var. serpentina |
Name authority | Nuttall: in J. Torrey and A. Gray, Fl. N. Amer. 1: 104. (1838) | (Tiehm & P. K. Holmgren) Al-Shehbaz & Windham: Harvard Pap. Bot. 12: 414. (2007) |
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