Draba alpina
Draba borealis
alpine Draba
boreal Draba, northern Draba, northern whitlow-grass
unbranched, (0.3–)0.5–1.7(–2.8) dm, pubescent throughout, trichomes simple and 2-rayed, 0.3–0.8 mm, with 3–5-rayed ones, 0.1–0.3 mm.
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).
rosulate; petiolate;
petiole base (not thickened), ciliate, (trichomes simple, 0.3–1 mm);
blade oblanceolate to obovate or lanceolate to oblong, 0.8–3(–4.5) cm × 2.5–6(–9) mm, margins entire, surfaces abaxially pubescent with stalked, 2–4-rayed trichomes, 0.1–0.5 mm, with simple ones (midvein obscure, not thickened), adaxially glabrous or sparsely pubescent with simple and stalked, 2–4-rayed trichomes.
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).
0.
(2 or) 3–7(–12);
sessile;
blade ovate, margins entire or dentate, surfaces pubescent as basal or adaxially with some simple trichomes.
6–18-flowered, ebracteate, considerably elongated in fruit;
rachis not flexuous, pubescent as stem.
(6–)8–20(–35)-flowered, ebracteate, elongated in fruit;
rachis not flexuous, pubescent as stem.
sepals (purplish tinged), narrowly ovate, 2.5–3 mm, pubescent, (trichomes simple and fewer, stalked, 2-rayed);
petals bright yellow, narrowly obovate, 3.5–5 × 1.7–2.5 mm;
anthers ovate, 0.3–0.4 mm.
sepals ovate, 2–3 mm, pubescent, (trichomes simple);
petals white, obovate, 4–6 × 2–3 mm;
anthers ovate, 0.3–0.5 mm.
ascending to divaricate-ascending, straight or, sometimes, slightly curved upwards, 4–14(–30) mm, pubescent, trichomes simple and 2–4-rayed.
divaricate or ascending, straight, (2–)4–8(–13) mm, pubescent as stem.
elliptic, plane, flattened, 6–10 × 2–3 mm;
valves glabrous or glabrescent, trichomes simple, (not confined to replum);
ovules 12–24 per ovary;
style 0.2–0.3 mm (stigma about as wide as style).
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.
(pale brown), ovoid, 0.9–1.3 × 0.6–0.9 mm.
oblong, 1–1.5 × 0.7–1 mm.
= 80.
= 64, 80.
Draba alpina
Draba borealis
The synonymy above includes two North American names overlooked by C. L. Hitchcock (1941) and R. C. Rollins (1993). Draba alpina was broadly delimited by O. E. Schulz (1927) and included 17 varieties, some of which (e.g., corymbosa, oxycarpa, pilosa) are recognized herein as distinct species. The name D. alpina was so misapplied that it was used for any circumpolar or alpine, scapose, yellow-flowered, perennial Draba. Various chromosome numbers (e.g., 2n = 64, 80, 112, 120; S. I. Warwick and I. A. Al-Shehbaz 2006) have been reported for the species. As circumscribed here, it has the narrow distribution outlined above and includes plants with 2n = 80. Reports of the species from Alaska, Canadian Northwest Territories and Yukon, Siberia, eastern Asia, Russian Far East, and the Central Asian republics are either suspect or very unlikely. The entire D. alpina complex (including the above three species, D. glacialis Adams, D. macounii, etc.) is in need of critical molecular, cytological, and morphological study.
(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.)
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