Draba lactea
Draba corymbosa
milky Draba, milky whitlow-grass
Baffin bay Draba, Baffin bay whitlow-grass, flat-top Draba
unbranched, 0.2–1.1(–1.5) dm,glabrous throughout or sparsely pubescent proximally, trichomes short-stalked, substellate, 2–8-rayed, (non-crisped), 0.5–0.3 mm.
unbranched, (0.05–)0.2–0.8(–1.5) dm, pubescent throughout, trichomes simple and 2-rayed, 0.4–1 mm, with 3–5-rayed ones, 0.05–0.4 mm, (sometimes trichomes mostly simple).
rosulate; petiolate;
petiole (persistent, strongly thickened), margin usually ciliate, (trichomes usually simple and 2-rayed, 0.3–1 mm);
blade oblanceolate to obovate, (0.3–)0.5–1.1(–1.7) cm × (1–)2–6 mm, margins usually entire, rarely denticulate, (sometimes ciliate), surfaces sometimes pubescent with stellate to subdendritic, 4–12-rayed, (non-crisped) trichomes, 0.1–0.4 mm, (midvein persistent, prominent, strongly thickened).
rosulate; petiolate;
petiole base and margin ciliate, (trichomes often course, simple, 0.4–1.3 mm);
blade oblanceolate to obovate, 0.6–1.8 cm × 1.5–5 mm, margins entire, surfaces pubescent, abaxially with stalked, 2–6-rayed trichomes, 0.2–0.6 mm, adaxially with primarily simple and stalked, 2-rayed trichomes, to 1.1 mm, with 3–5-rayed ones, 0.2–0.4 mm.
0 (or, rarely, 1 as a bract).
0.
2–8(–12)-flowered, ebracteate, elongated in fruit;
rachis not flexuous, usually glabrous, rarely sparsely pubescent as stem basally.
2–9(–12)-flowered, ebracteate, (corymbose), slightly elongated in fruit;
rachis not flexuous, pubescent as stem.
sepals ovate, 1.8–3 mm, usually glabrous, rarely sparsely pubescent subapically, (trichomes simple);
petals white, obovate, 3–5 × 1.8–3 mm;
anthers ovate, 0.3–0.4 mm.
sepals (grayish green), broadly ovate, 2.2–3 mm, pubescent, (trichomes simple, to 1 mm, sometimes with stalked, smaller, 2–4-rayed ones);
petals (broadly patent), yellow, obovate, 4–6 × 3–5 mm;
anthers ovate, 0.3–0.4 mm.
divaricate-ascending, straight, (1–)2–5(–10) mm, glabrous.
divaricate-ascending, straight or slightly curved upward, 4–11(–16) mm, pubescent, trichomes simple and 2–4-rayed.
oblong to elliptic-lanceolate or ovate to broadly so, plane, flattened, 4–8 × (1.5–)2–3 mm;
valves glabrous;
ovules (10–)14–22(–26) per ovary;
style 0.1–0.4 mm.
oblong or ovate, plane, flattened, 6–12 × 3.5–5.5 mm;
valves pubescent or puberulent, trichomes simple, 0.1–0.4 mm, (sometimes with short-stalked, 2- or 3-rayed ones);
ovules 12–24 per ovary;
style 0.6–1 mm (stigma distinctly wider than style).
ovoid, 0.8–1.1 × 0.5–0.6 mm.
(brown), ovoid, 1–1.3 × 0.6–0.9 mm.
= 32, 48.
= 128, 144.
Draba lactea
Draba corymbosa
T. W. Böcher (1966) postulated that Draba lactea originated from hybridization between D. fladnizensis and D. nivalis, but A.-C. Scheen et al. (2002) showed that it is more closely allied to D. subcapitata. By contrast, H. H. Grundt et al. (2004) concluded that hexaploid D. lactea originated from tetraploids of the same species, which in turn originated from the diploid D. palanderiana lineage. They suggested that D. lactea probably originated multiple times in the Beringian area and migrated to reach its present circumpolar distribution. The hexaploids are distributed throughout the species range, whereas the tetraploids are known only from Alaska and the Russian Far East (Grundt et al. 2005b).
Draba fernaldiana, which was collected from Southampton Island (Nunavut), was not mentioned by R. C. Rollins (1993). The plants are completely glabrous except for leaf margins, which are ciliate with simple and sparse 2-rayed trichomes. The taxon resembles some forms of D. lactea and is tentatively herein included within that species. The only conflict in such placement is petal color, which was listed in the original description of D. fernaldiana as pale yellow instead of white.
Glabrous or glabrescent forms of Draba lactea are quite common in the Canadian Arctic Archipelago, whereas pubescent forms predominate in Alaska and the Russian Far East.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Draba corymbosa, which is 16-ploid or 18-ploid with x = 8, is an extremely variable species of polyphyletic, allopolyploid origin. Most individuals appear to have decaploid D. alpina (2n = 80) in their parentage, but the other genomes are provided by hexaploid (2n = 48) and octoploid (2n = 64) species (C. Brochmann et al. 1993). O. E. Schulz reduced D. corymbosa to a variety of D. alpina; R. C. Rollins (1993) treated it as a distinct species. Draba corymbosa is distinguished from D. alpina by having pubescent or puberulent (versus glabrous or glabrescent) fruits, corymbose (versus usually elongated) fruiting racemes, and abaxial leaf blade surfaces always lacking (versus usually with some) simple trichomes.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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