Flora of North America species comparison

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Draba lactea

Draba crassa

milky Draba, milky whitlow-grass

thickleaf Draba
Habit Perennials; (cespitose); caudex branched (with persistent petiole remains, branches sometimes terminating in sterile rosettes); scapose. Perennials; (cespitose); caudex simple or branched (well-developed, with persistent leaf bases); not 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.

(decumbent to ascending), unbranched, (0.4–)0.6–1.3(–1.5) dm, usually glabrous proximally, rarely sparsely pubescent, pubescent distally, trichomes simple and short-stalked, 2-rayed, (crisped), 0.1–0.6(–0.8) 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; petiolate;

petiole ciliate, (trichomes mostly simple, 0.3–0.8 mm);

blade oblanceolate, 2–6(–7) cm × 2.5–8(–10) mm, margins entire, (pubescent as petiole), surfaces glabrous.
Cauline leaves

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

2–4(–6);

sessile;

blade ovate to oblong, margins entire, (ciliate, trichomes simple and stalked, 2-rayed).
Racemes

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

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

(4–)8–20(–25)-flowered, ebracteate, elongated in fruit;

rachis not flexuous, pubescent, trichomes simple and short-stalked, 2-rayed, (crisped), (0.1–0.8 mm).
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 (green tinged purplish), ovate to oblong, 2–3(–3.3) mm, pubescent, (trichomes simple and 2-rayed);

petals yellow, spatulate to subobovate, 3.5–5(–6) × (2–) 2.5–3.5(–4) mm;

anthers ovate, 0.5–0.6 mm.
Fruiting pedicels

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

divaricate-ascending, straight, 5–10(–15) mm, pubescent as rachis.
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 ovate-lanceolate, slightly twisted, flattened, (7–)8–14 × 3–5 mm;

valves glabrous;

ovules 16–20 per ovary;

style (0.4–)0.7–1.2(–1.5) mm.
Seeds

ovoid, 0.8–1.1 × 0.5–0.6 mm.

oblong, 1.2–1.7 × 0.8–1.1 mm.
2n

= 32, 48.

= 24.

Draba lactea

Draba crassa
Phenology Flowering Jun–Aug. Flowering Jul–Aug.
Habitat Rock outcrops, talus, rocky hillsides and ridges, open gravelly areas, seepage swales, meadows Rock outcrops and talus, alpine tundra, rocky meadows
Elevation 0-2000 m (0-6600 ft) 2900-4300 m (9500-14100 ft)
Distribution
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]
from FNA
CO; MT; NM; UT; WY
[WildflowerSearch map]
[BONAP county map]
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 crassa is easily recognized by its combination of fleshy, distinctly petiolate leaves with glabrous surfaces and mostly decumbent flowering/fruiting stems. N. H. Holmgren (2005b) indicated that it has 52 seeds per fruit (26 per locule), but in the plants we examined, the seed count did not exceed 20 per fruit.

(Discussion copyrighted by Flora of North America; reprinted with permission.)
Source FNA vol. 7, p. 316. FNA vol. 7, p. 302.
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. 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
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. 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. 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
Synonyms D. allenii, D. boecheri, D. fernaldiana D. chrysantha var. crassa
Name authority Adams: Mém. Soc. Imp. Naturalistes Moscou 5: 104. (1817) Rydberg: Mem. New York Bot. Gard. 1: 182. (1900)
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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