Draba incerta |
Draba borealis |
|
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whitlow-wort, Yellowstone Draba, Yellowstone Draba whitlow-wort, Yellowstone whitlow-grass, Yellowstone whitlow-wort |
boreal Draba, northern Draba, northern whitlow-grass |
|
Habit | Perennials; (cespitose, often pulvinate); caudex branched (dense with persistent leaf remains, branches sometimes terminating in sterile rosettes); scapose. | Perennials; caudex branched (branches usually slender, elongated, rhizomatous, sometimes with persistent leaf bases); not scapose. |
Stems | unbranched, (0.2–)0.4–1.4(–2.1) dm, often pubescent throughout, sometimes glabrous distally, trichomes often simple and 2–5-rayed, 0.1–0.5 mm, (sometimes with mostly subpectinate ones). |
usually unbranched, rarely branched, (0.4–)1–3.6(–5.5) dm, often hirsute proximally, trichomes usually simple and 2-rayed, 0.5–1.1 mm, with short-stalked, 3–8-rayed ones, 0.1–0.4 mm (rarely simple trichomes absent distally). |
Basal leaves | rosulate; petiolate; petiole (0–1 cm), ciliate throughout; blade narrowly oblanceolate to linear, (0.4–)0.6–1.7(–2.5) cm × (1–)1.5–3.5(–5) mm, margins entire, (ciliate, trichomes usually simple, rarely 2-rayed, 0.2–1.1 mm), surfaces usually pubescent with short-stalked, pectinate trichomes, 0.15–0.5 mm, sometimes also with 4–6-rayed ones, (midvein usually obscure abaxially), sometimes glabrous adaxially. |
rosulate; blade ovate or obovate to oblanceolate, (0.5–)1–4.2(–6) cm × 3–10(–25) mm, margins dentate or denticulate, surfaces pubescent, trichomes short-stalked, cruciform, or (2–)4–6-rayed, 0.2–0.6 mm (principal rays usually simple, rarely 1 or 2 with a lateral branch, sometimes appearing to 10-rayed). |
Cauline leaves | usually 0 (or 1, as a bract); sessile; blade linear to oblong, margins entire, surfaces pubescent as basal. |
(2 or) 3–7(–12); sessile; blade ovate, margins entire or dentate, surfaces pubescent as basal or adaxially with some simple trichomes. |
Racemes | 3–14(–30)-flowered, usually ebracteate, rarely proximalmost flowers bracteate, elongated in fruit; rachis not flexuous, glabrous or pubescent as stem. |
(6–)8–20(–35)-flowered, ebracteate, elongated in fruit; rachis not flexuous, pubescent as stem. |
Flowers | sepals broadly ovate, 2.5–3.5(–4) mm, pubescent, (trichomes simple and 2- or 3-rayed); petals yellow (fading white), oblanceolate to obovate, 4–6 × 1.5–2.5 mm; anthers ovate, 0.3–0.5 mm. |
sepals ovate, 2–3 mm, pubescent, (trichomes simple); petals white, obovate, 4–6 × 2–3 mm; anthers ovate, 0.3–0.5 mm. |
Fruiting pedicels | ascending, straight, (2.5–)4–11(–27) mm, glabrous or pubescent, trichomes 2–5-rayed or pectinate. |
divaricate or ascending, straight, (2–)4–8(–13) mm, pubescent as stem. |
Fruits | broadly ovate to lanceolate, plane, flattened, 5–9(–11) × 2–4 mm; valves glabrous or puberulent, trichomes simple and 2-rayed, 0.05–0.3 mm; ovules 8–16(–20) per ovary; style 0.2–0.9 mm. |
ovate to broadly oblong or lanceolate, slightly twisted or plane, flattened, (5–)7–12 × 2.5–4.5 mm; valves pubescent, trichomes simple and short-stalked, 2–4-rayed, 0.1–0.4 mm; ovules 16–28(–30) per ovary; style 0.2–0.6(–0.8) mm, glabrous. |
Seeds | oblong, 1.1–1.5 × 0.7–1 mm. |
oblong, 1–1.5 × 0.7–1 mm. |
2n | = 112. |
= 64, 80. |
Draba incerta |
Draba borealis |
|
Phenology | Flowering Jun–Aug. | Flowering Jun–Jul. |
Habitat | Rock outcrops, talus, gravelly areas, tundra | Rock outcrops and talus, gravelly terraces, meadows, forest edges and thickets, roadsides, grassy areas, alpine tundra |
Elevation | 0-3300 m (0-10800 ft) | 0-2400 m (0-7900 ft) |
Distribution |
AK; CO; ID; MT; NV; UT; WA; WY; AB; BC; QC; YT
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AK; AB; BC; NT; NU; YT; e Asia (Japan, Russian Far East) |
Discussion | Draba incerta was shown by G. A. Mulligan (1972) to be sexually reproducing and 14-ploid with x = 8. It is often confused with the apomict D. oligosperma (2n = 32, 64). Draba incerta is readily separated from D. oligosperma by having well-formed (versus abortive) anthers and pollen, stalked (versus sessile) leaf trichomes, and ciliate (versus non-ciliate) basal leaves with obscure (versus prominent) midveins. Although both species have leafless scapes, one often finds a bract adnate to, or subtending, the proximalmost pedicel in D. incerta. Draba incerta is found near sea level in Alaska. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Draba borealis is highly variable in leaf and stem indumentum, leaf shape and margin, number of cauline leaves, and fruit shape, size, and twisting. North American plants yielded decaploid chromosome counts; octoploid populations were reported from the Russian Far East. This suggests that more than one taxon is present, and the species is much in need of detailed molecular, cytogenetic, and morphological study. In the absence of flowers, Draba borealis is occasionally confused with some forms of D. aurea. The latter usually has proximally bracteate (versus ebracteate) racemes, generally longer styles [0.5–1.5(–1.7) versus 0.2–0.6(–0.8) mm], and more ovules [28–38(–44) versus 16–28(–30)] per ovary. Draba borealis occasionally is confused with D. glabella, but the latter has pectinate-stellate trichomes on abaxial leaf blade surfaces. R. C. Rollins (1993) indicated that D. borealis occurs in Colorado, but we have not seen any material from the United States outside of Alaska. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Source | FNA vol. 7, p. 313. | FNA vol. 7, p. 296. |
Parent taxa | Brassicaceae > tribe Arabideae > Draba | Brassicaceae > tribe Arabideae > Draba |
Sibling taxa | ||
Synonyms | D. exalata, D. incerta var. laevicapsula, D. incerta var. peasei, D. laevicapsula, D. peasei | D. borealis var. maxima, D. maxima, D. unalaschkiana |
Name authority | Payson: Amer. J. Bot. 4: 261. (1917) | de Candolle: Syst. Nat. 2: 342. (1821) |
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