Draba lactea |
Draba pedicellata |
|
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milky Draba, milky whitlow-grass |
Cusick's Draba, rocky-slope Draba, rocky-slope whitlow-grass, stalk whitlow-cress |
|
Habit | Perennials; (cespitose); caudex branched (with persistent petiole remains, branches sometimes terminating in sterile rosettes); scapose. | Perennials; (loosely cespitose); caudex branched (with persistent leaf bases, branches sometimes terminating in sterile rosettes); scapose. |
Stems | 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, (0.15–)0.3–1.3(–1.6) dm, pubescent proximally, glabrous or nearly so distally, trichomes 2- or 3-rayed and simple, 0.1–1 mm. |
Basal leaves | 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; subsessile; blade oblanceolate to obovate, 0.4–1.6(–2) cm × 2–4(–6) mm, margins entire, (not ciliate), surfaces pubescent with stalked, 2–4-rayed trichomes, 0.2–0.9 mm, rarely adaxially with simple trichomes, (midvein obscure abaxially). |
Cauline leaves | 0 (or, rarely, 1 as a bract). |
0. |
Racemes | 2–8(–12)-flowered, ebracteate, elongated in fruit; rachis not flexuous, usually glabrous, rarely sparsely pubescent as stem basally. |
3–20(–27)-flowered, ebracteate, slightly to considerably elongated in fruit; rachis straight or flexuous, usually glabrous, rarely pubescent, trichomes simple and 2–4-rayed. |
Flowers | 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 broadly ovate, 1.8–2.5 mm, glabrous or pubescent, (trichomes simple and branched); petals yellow, spatulate, 3.5–5.5 × 1.5–2.2 mm; anthers ovate, 0.4–0.5 mm. |
Fruiting pedicels | divaricate-ascending, straight, (1–)2–5(–10) mm, glabrous. |
divaricate to horizontal, straight or curved upward (expanded basally or not), 4–9(–13) mm, glabrous or pubescent, trichomes simple and 2–4-rayed. |
Fruits | 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. |
lanceolate to ellipsoid or ovoid, plane (not curved), inflated or slightly flattened, (4.2–)5.3–10(–13) × 2.5–4.5(–5.5) mm; valves glabrous or pubescent, trichomes simple and short-stalked, 2-rayed, 0.05–0.3 mm; ovules 8–16 per ovary; style 0.3–1(–1.2) mm. |
Seeds | ovoid, 0.8–1.1 × 0.5–0.6 mm. |
oblong, 1.2–1.6 × 0.7–0.9 mm. |
2n | = 32, 48. |
= 20. |
Draba lactea |
Draba pedicellata |
|
Phenology | Flowering Jun–Aug. | Flowering May–Jul. |
Habitat | Rock outcrops, talus, rocky hillsides and ridges, open gravelly areas, seepage swales, meadows | Rock outcrops, talus, steep gravel slopes in pinyon-juniper, mixed conifer, and subalpine meadow communities |
Elevation | 0-2000 m (0-6600 ft) | 2300-3800 m (7500-12500 ft) |
Distribution |
AK; NL; NT; NU; QC; YT; Greenland; Europe (n Finland, Norway, w Sweden); Asia (Russian Far East, c, n Siberia); Atlantic Islands (Iceland); circumpolar |
NV; UT
|
Discussion | 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 pedicellata is known from Elko, Eureka, Nye, and White Pine counties in northeastern Nevada and to Tooele County in northwestern Utah. It was considered a variety of D. cusickii by R. C. Rollins (1993); chromosome number, morphology, and geographic distribution suggest a closer relationship to D. sphaeroides. For a detailed discussion and comparison of these species, consult M. D. Windham (2004). N. H. Holmgren (2005b) divided D. pedicellata into two varieties: var. pedicellata, which is found on limestone throughout the species range, and var. wheelerensis, which is found on non-calcareous substrates in White Pine County. Although var. wheelerensis has slightly more spreading pedicels on somewhat more flexuous rachises, it appears to be little more than a dwarf alpine form of the species. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Source | FNA vol. 7, p. 316. | FNA vol. 7, p. 328. |
Parent taxa | Brassicaceae > tribe Arabideae > Draba | Brassicaceae > tribe Arabideae > Draba |
Sibling taxa | ||
Synonyms | D. allenii, D. boecheri, D. fernaldiana | D. cusickii var. pedicellata, D. pedicellata var. wheelerensis |
Name authority | Adams: Mém. Soc. Imp. Naturalistes Moscou 5: 104. (1817) | (Rollins & R. A. Price) Windham: Madroño 50: 221. (2004) |
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