Flora of North America species comparison

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Draba petrophila

Draba lactea

Santa Rita Mountain Draba, Santa Rita Mountain whitlowgrass, Santa Rita whitlow grass

milky Draba, milky whitlow-grass
Habit Perennials; (cespitose, long-lived); caudex simple or branched (covered with persistent petioles), not scapose. Perennials; (cespitose); caudex branched (with persistent petiole remains, branches sometimes terminating in sterile rosettes); scapose.
Stems

usually unbranched, rarely branched, 0.3–1.9(–2.8) dm, moderately to densely hirsute throughout, trichomes simple, 0.2–1.3 mm, with short-stalked to subsessile, cruciform, 0.02–0.4 mm, and 2-rayed ones, 0.3–0.9 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

rosulate; petiolate;

petiole ciliate, (trichomes simple, 0.4–1.5 mm);

blade oblanceolate, 1–5(–6) cm × 2–5(–10) mm, margins usually entire, rarely denticulate, surfaces pubescent, abaxially with stalked, cruciform trichomes, 0.07–0.5 mm, adaxially often similar, sometimes with fewer, simple and 2-rayed trichomes, 0.4–1.3 mm.

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

3–10;

sessile;

blade ovate to lanceolate or oblong, margins entire or denticulate, surfaces pubescent as basal.

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

10–37(–58)-flowered, ebracteate, elongated in fruit;

rachis not flexuous, pubescent as stem.

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

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

sepals oblong, 2–3.5 mm, pubescent, (trichomes simple and 2-rayed);

petals yellow, oblanceolate, 3.5–6 × 1.2–1.8 mm;

anthers oblong, 0.8–1 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

divaricate-ascending, straight, 4–10 mm, pubescent throughout, trichomes simple (0.1–0.5 mm) and subsessile, 2–4-rayed, (0.03–0.2 mm).

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

lanceolate to elliptic, often strongly twisted, flattened, 5–11 × 2–3 mm;

valves puberulent at least along margin, trichomes simple, antrorse, 0.03–0.15 mm;

ovules 14–24 per ovary;

style 0.8–1.8(–2.5) 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

ovoid, 1–1.4 × 0.6–0.9 mm.

ovoid, 0.8–1.1 × 0.5–0.6 mm.
2n

= 32, 48.

Draba petrophila

Draba lactea
Phenology Flowering Jul–Sep. Flowering Jun–Aug.
Habitat Crevices, ledges of cliffs Rock outcrops, talus, rocky hillsides and ridges, open gravelly areas, seepage swales, meadows
Elevation 1200-2800 m (3900-9200 ft) 0-2000 m (0-6600 ft)
Distribution
from FNA
AZ
[WildflowerSearch map]
[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 petrophila is often broadly circumscribed to include the taxon herein called D. viridis. For a discussion of the differences between these species and the closely related D. helleriana, see I. A. Al-Shehbaz and M. D. Windham (2007). Draba petrophila, in the strict sense, is known only from Cochise, Pima, and Santa Cruz counties in southeastern Arizona.

(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. 329. 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. 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. 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. helleriana var. blumeri, D. helleriana var. petrophila D. allenii, D. boecheri, D. fernaldiana
Name authority Greene: Pittonia 4: 17. (1899) 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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