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Mcdonald's rock-cress

Eschscholtz's hairy rock-cress, Eschscholtz's rockcress, hairy rockcress, Pacific coast rockcress

Habit Perennials; (caudex simple or branched, covered with persistent petiolar remains); usually glabrous, rarely sparsely pubescent, trichomes simple, (to 0.5 mm), not bulbous-based. Biennials or perennials; (caudex branched); usually densely hirsute (at least basally), trichomes simple or stalked, forked, sometimes glabrescent with mostly simple ones.
Stems

simple or few from base (caudex), erect, unbranched, (0.6–)1.5–3(–4) dm, (glabrous).

simple or several from base (rosette), erect, often branched distally, 2–7(–10) dm, (hirsute basally, trichomes simple and minutely stalked, forked, rarely almost exclusively glabrous).

Basal leaves

petiole 0.3–1.5 cm;

blade oblanceolate to obovate, (0.5–)1–3(–4) cm × (2–)3–6(–10) mm, margins entire, repand, or obtusely dentate, apex obtuse, surfaces sometimes with individual trichomes terminating some or all leaf teeth.

petiole 0.7–3 cm, (ciliate or not);

blade broadly spatulate to narrowly oblanceolate, 1.2–10 cm × 7–30 mm, margins entire or dentate, apex obtuse or acute, surfaces usually pubescent, sometimes glabrous, trichomes simple, forked and stalked, stellate.

Cauline leaves

(2 or) 3–5 (or 6);

blade oblong, 0.3–1(–1.2) cm × 1–3 mm, base not auriculate, margins entire or repand, apex obtuse, surfaces glabrous.

(2–)4–12(–18), (well-spaced or, rarely, overlapping);

blade ovate to oblong or lanceolate, 1.5–6.5(–10) cm × 5–30 mm, base auriculate, margins dentate or entire, apex acute or obtuse, surfaces sparsely hirsute or glabrous.

Racemes

simple, (dense).

simple or branched.

Flowers

sepals (purple), oblong, 4–8 × 1.5–2.5 mm, lateral pair saccate basally;

petals purple, spatulate, 8–16 × 2–5 mm, apex obtuse;

filaments 4–8 mm;

anthers oblong, 1.5–2 mm.

sepals oblong, 3.5–5 × 1.2–2 mm, lateral pair saccate basally;

petals white, rarely pink, linear-oblanceolate or narrowly spatulate, (5.5–) 6.5–9(–10) × 1.5–3 mm, apex obtuse;

filaments 3.5–6 mm;

anthers oblong, 0.7–1 mm.

Fruiting pedicels

ascending to suberect, 3–10(–13) mm.

erect to erect-ascending, 3.5–10(–15) mm, (glabrous or sparsely pubescent).

Fruits

ascending to suberect, not torulose, sometimes slightly curved, 2–4 cm × 1.5–2 mm;

valves each with prominent midvein extending full length;

ovules 20–34 per ovary;

style 0.3–1.5 mm.

erect to erect-ascending, (often appressed to rachis), torulose, 3.5–6.5 cm × 1.2–1.8(–2) mm;

valves each with prominent midvein extending full length or to middle;

ovules 54–80 per ovary;

style (0.1–)0.3–1 mm.

Seeds

narrowly winged distally or, rarely, not winged, oblong, 1.5–2.2 × 1–1.3 mm, wing 0.1–0.2 mm wide.

usually narrowly winged throughout or only distally, rarely not winged, oblong or suborbicular, 1–1.8 × 0.9–1.3 mm;

wing to 0.2 mm wide distally.

2n

= 32, 64.

Arabis mcdonaldiana

Arabis eschscholtziana

Phenology Flowering May–Jun. Flowering (Apr-)May–Jul.
Habitat Serpentine scrap and slopes, red serpentinized soil Rocky slopes, crevices, and ledges, meadows, moist banks and grounds, granitic soil, wooded slopes
Elevation 200-1800 m (700-5900 ft) 0-2800 m (0-9200 ft)
Distribution
from FNA
CA; OR
[WildflowerSearch map]
from FNA
AK; CA; ID; MT; NV; OR; UT; WA; WY; AB; BC; YT
[WildflowerSearch map]
[BONAP county map]
Discussion

Of conservation concern.

Arabis mcdonaldiana is known in California from Del Norte, Mendocino, and Siskiyou counties, and in Oregon from Curry and Jackson counties. It is in the Center for Plant Conservation’s National Collection of Endangered Plants.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

G. A. Mulligan (1996) recognized Arabis eschscholtziana as a distinct species; R. C. Rollins (1941, 1993) treated it as a variety of A. hirsuta. As discussed under A. pycnocarpa, A. hirsuta does not occur in North America, and the characters separating all three species (see key to species), as well as the different ploidy levels, support Mulligan’s conclusion.

Both M. Hopkins (1937) and R. C. Rollins (1941, 1993) recognized the glabrous or subglabrate forms native to North America as a distinct variety, var. glabrata; G. A. Mulligan (1996) did not accord such forms any taxonomic status. Glabrous and subglabrate forms occur in both Arabis eschscholtziana and A. pycnocarpa and sometimes even within a population that has moderately to densely pubescent forms. I support Mulligan’s view in not recognizing the glabrous forms as an infraspecific taxon.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Source FNA vol. 7, p. 265. FNA vol. 7, p. 261.
Parent taxa Brassicaceae > tribe Arabideae > Arabis Brassicaceae > tribe Arabideae > Arabis
Sibling taxa
A. aculeolata, A. alpina, A. blepharophylla, A. caucasica, A. crucisetosa, A. eschscholtziana, A. furcata, A. georgiana, A. modesta, A. nuttallii, A. olympica, A. oregana, A. patens, A. pycnocarpa
A. aculeolata, A. alpina, A. blepharophylla, A. caucasica, A. crucisetosa, A. furcata, A. georgiana, A. mcdonaldiana, A. modesta, A. nuttallii, A. olympica, A. oregana, A. patens, A. pycnocarpa
Synonyms A. blepharophylla var. mcdonaldiana, A. serpentinicola A. hirsuta subsp. eschscholtziana, A. hirsuta var. eschscholtziana, A. hirsuta var. glabrata, A. ovata var. glabrata, A. pycnocarpa var. glabrata, A. rupestris, A. stelleri var. eschscholtziana, Turritis spathulata
Name authority Eastwood: Bull. Torrey Bot. Club 30: 488, unnumb. fig. (p. 489). (1903) Andrzejowski: in C. F. von Ledebour, Fl. Altaica 3: 25. (1831)
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