Flora of North America species comparison

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Draba hitchcockii

Draba lactea

lost river Draba

milky Draba, milky whitlow-grass
Habit Perennials; (densely cespitose); caudex branched (densely covered with persistent leaves, branches sometimes terminating in sterile rosettes); scapose. Perennials; (cespitose); caudex branched (with persistent petiole remains, branches sometimes terminating in sterile rosettes); scapose.
Stems

unbranched, (0.1–)0.3–1(–1.3) dm, hirsute throughout, trichomes simple, 0.4–1 mm, and 2–4-rayed, 0.1–0.6 mm.

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

(densely imbricate); rosulate;

sessile;

blade narrowly oblanceolate to oblong-linear, 0.3–1.2(–1.5) cm × 1–2 mm, margins entire, (ciliate, trichomes simple, 0.3–1.2 mm), surfaces pubescent abaxially with stalked, 2–4-rayed trichomes, 0.08–0.45 mm, (midvein obscure), adaxially glabrous proximally, sparsely pubescent distally with mostly simple trichomes.

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

0.

0 (or, rarely, 1 as a bract).
Racemes

4–15-flowered, ebracteate, elongated in fruit;

rachis not flexuous, hirsute as stem.

2–8(–12)-flowered, ebracteate, elongated in fruit;

rachis not flexuous, usually glabrous, rarely sparsely pubescent as stem basally.
Flowers

sepals oblong, 2.5–3.5 mm, hirsute, (trichomes simple and stalked, 2–4-rayed);

petals white, obovate, 5–6.5 × 2–3.5 mm;

anthers ovate, 0.5–0.6 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–)4–13(–18) mm, hirsute as stem.

divaricate-ascending, straight, (1–)2–5(–10) mm, glabrous.
Fruits

ovate to broadly oblong or elliptic, plane, flattened, (3–)4–7(–10) × (2.5–)3.5–5 mm;

valves pubescent, trichomes simple and short-stalked, 2(–4)-rayed, 0.06–0.5 mm;

ovules 8–12 per ovary;

style (0.8–)1–1.7(–2) 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, 1.4–1.8 × 0.8–1 mm.

ovoid, 0.8–1.1 × 0.5–0.6 mm.
2n

= 54.

= 32, 48.

Draba hitchcockii

Draba lactea
Phenology Flowering May–Jun. Flowering Jun–Aug.
Habitat Limestone outcrops and gravelly soil Rock outcrops, talus, rocky hillsides and ridges, open gravelly areas, seepage swales, meadows
Elevation 1800-2200 m (5900-7200 ft) 0-2000 m (0-6600 ft)
Distribution
from FNA
ID
[BONAP county map]
from FNA
AK; NL; NT; NU; QC; YT; Greenland; Europe (n Finland, Norway, w Sweden); Asia (Russian Far East, c, n Siberia); Atlantic Islands (Iceland); circumpolar
[BONAP county map]
Discussion

Draba hitchcockii is known from the Lost River Range in Butte and Custer counties. Based on morphological and chromosomal evidence, M. D. Windham (2004) suggested that it may be an allopolyploid resulting from hybridization between D. oreibata and D. paysonii. Draba hitchcockii is superficially similar to D. jaegeri, a taxon known from the Charleston Mountains of Clark County, Nevada. Both are cespitose perennials with relatively large, white flowers and a chromosome number (2n = 54) otherwise unknown in Draba (Windham). Features distinguishing these two taxa are provided in the discussion of 51. D. jaegeri.

(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. 311. FNA vol. 7, p. 316.
Parent taxa Brassicaceae > tribe Arabideae > Draba Brassicaceae > tribe Arabideae > Draba
Sibling taxa
D. abajoensis, D. albertina, D. aleutica, D. alpina, D. aprica, D. arabisans, D. arctica, D. arctogena, D. argyrea, D. arida, D. asprella, D. asterophora, D. aurea, D. aureola, D. bifurcata, D. borealis, D. brachycarpa, D. brachystylis, D. breweri, D. burkei, D. californica, D. cana, D. carnosula, D. chamissonis, D. cinerea, D. corrugata, D. corymbosa, D. crassa, D. crassifolia, D. cruciata, D. cuneifolia, D. cusickii, D. cyclomorpha, D. daviesiae, D. densifolia, D. exunguiculata, D. fladnizensis, D. glabella, D. globosa, D. graminea, D. grandis, D. grayana, D. heilii, D. helleriana, D. howellii, D. incana, D. incerta, D. incrassata, D. inexpectata, D. jaegeri, D. juvenilis, D. kassii, D. kluanei, D. lactea, D. lemmonii, D. lonchocarpa, D. longisquamosa, D. macounii, D. maguirei, D. malpighiacea, D. micropetala, D. mogollonica, D. monoensis, D. mulliganii, D. murrayi, D. nemorosa, D. nivalis, D. norvegica, D. novolympica, D. oblongata, D. ogilviensis, D. oligosperma, D. oreibata, D. oxycarpa, D. palanderiana, D. pauciflora, D. paucifructa, D. paysonii, D. pectinipila, D. pedicellata, D. pennellii, D. petrophila, D. pilosa, D. platycarpa, D. porsildii, D. praealta, D. pterosperma, D. ramosissima, D. ramulosa, D. rectifructa, D. reptans, D. ruaxes, D. santaquinensis, D. saxosa, D. scotteri, D. serpentina, D. sharsmithii, D. sibirica, D. sierrae, D. simmonsii, D. smithii, D. sobolifera, D. spectabilis, D. sphaerocarpa, D. sphaeroides, D. standleyi, D. stenoloba, D. stenopetala, D. streptobrachia, D. streptocarpa, D. subalpina, D. subcapitata, D. subumbellata, D. trichocarpa, D. ventosa, D. verna, D. viridis, D. weberi, D. yukonensis, D. zionensis
D. abajoensis, D. albertina, D. aleutica, D. alpina, D. aprica, D. arabisans, D. arctica, D. arctogena, D. argyrea, D. arida, D. asprella, D. asterophora, D. aurea, D. aureola, D. bifurcata, D. borealis, D. brachycarpa, D. brachystylis, D. breweri, D. burkei, D. californica, D. cana, D. carnosula, D. chamissonis, D. cinerea, D. corrugata, D. corymbosa, D. crassa, D. crassifolia, D. cruciata, D. cuneifolia, D. cusickii, D. cyclomorpha, D. daviesiae, D. densifolia, D. exunguiculata, D. fladnizensis, D. glabella, D. globosa, D. graminea, D. grandis, D. grayana, D. heilii, D. helleriana, D. hitchcockii, D. howellii, D. incana, D. incerta, D. incrassata, D. inexpectata, D. jaegeri, D. juvenilis, D. kassii, D. kluanei, D. lemmonii, D. lonchocarpa, D. longisquamosa, D. macounii, D. maguirei, D. malpighiacea, D. micropetala, D. mogollonica, D. monoensis, D. mulliganii, D. murrayi, D. nemorosa, D. nivalis, D. norvegica, D. novolympica, D. oblongata, D. ogilviensis, D. oligosperma, D. oreibata, D. oxycarpa, D. palanderiana, D. pauciflora, D. paucifructa, D. paysonii, D. pectinipila, D. pedicellata, D. pennellii, D. petrophila, D. pilosa, D. platycarpa, D. porsildii, D. praealta, D. pterosperma, D. ramosissima, D. ramulosa, D. rectifructa, D. reptans, D. ruaxes, D. santaquinensis, D. saxosa, D. scotteri, D. serpentina, D. sharsmithii, D. sibirica, D. sierrae, D. simmonsii, D. smithii, D. sobolifera, D. spectabilis, D. sphaerocarpa, D. sphaeroides, D. standleyi, D. stenoloba, D. stenopetala, D. streptobrachia, D. streptocarpa, D. subalpina, D. subcapitata, D. subumbellata, D. trichocarpa, D. ventosa, D. verna, D. viridis, D. weberi, D. yukonensis, D. zionensis
Synonyms D. allenii, D. boecheri, D. fernaldiana
Name authority Rollins: J. Arnold Arbor. 64: 500. (1983) Adams: Mém. Soc. Imp. Naturalistes Moscou 5: 104. (1817)
Web links 
Unless otherwise noted, all data comes from the online version of the Flora of North America, who have made most of their content available via a Creative Commons license (CC BY 4.0).



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