Draba incerta |
Draba lactea |
|
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whitlow-wort, Yellowstone Draba, Yellowstone Draba whitlow-wort, Yellowstone whitlow-grass, Yellowstone whitlow-wort |
milky Draba, milky whitlow-grass |
|
Habit | Perennials; (cespitose, often pulvinate); caudex branched (dense with persistent leaf remains, branches sometimes terminating in sterile rosettes); scapose. | Perennials; (cespitose); caudex branched (with persistent petiole remains, branches sometimes terminating in sterile rosettes); 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). |
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. |
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; 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). |
Cauline leaves | usually 0 (or 1, as a bract); sessile; blade linear to oblong, margins entire, surfaces pubescent as basal. |
0 (or, rarely, 1 as a bract). |
Racemes | 3–14(–30)-flowered, usually ebracteate, rarely proximalmost flowers bracteate, elongated in fruit; rachis not flexuous, glabrous or pubescent as stem. |
2–8(–12)-flowered, ebracteate, elongated in fruit; rachis not flexuous, usually glabrous, rarely sparsely pubescent as stem basally. |
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, 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. |
Fruiting pedicels | ascending, straight, (2.5–)4–11(–27) mm, glabrous or pubescent, trichomes 2–5-rayed or pectinate. |
divaricate-ascending, straight, (1–)2–5(–10) mm, glabrous. |
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. |
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. |
Seeds | oblong, 1.1–1.5 × 0.7–1 mm. |
ovoid, 0.8–1.1 × 0.5–0.6 mm. |
2n | = 112. |
= 32, 48. |
Draba incerta |
Draba lactea |
|
Phenology | Flowering Jun–Aug. | Flowering Jun–Aug. |
Habitat | Rock outcrops, talus, gravelly areas, tundra | Rock outcrops, talus, rocky hillsides and ridges, open gravelly areas, seepage swales, meadows |
Elevation | 0-3300 m (0-10800 ft) | 0-2000 m (0-6600 ft) |
Distribution |
AK; CO; ID; MT; NV; UT; WA; WY; AB; BC; QC; YT
|
AK; NL; NT; NU; QC; YT; Greenland; Europe (n Finland, Norway, w Sweden); Asia (Russian Far East, c, n Siberia); Atlantic Islands (Iceland); circumpolar |
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.) |
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.) |
Source | FNA vol. 7, p. 313. | FNA vol. 7, p. 316. |
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. allenii, D. boecheri, D. fernaldiana |
Name authority | Payson: Amer. J. Bot. 4: 261. (1917) | Adams: Mém. Soc. Imp. Naturalistes Moscou 5: 104. (1817) |
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