Arabis alpina
Arabis nuttallii
alpine rockcress, arabis alpina
Nuttall's rockcress
usually simple from base, erect to ascending, often branched proximally, (0.6–)1–2(–2.5) dm.
simple or few to numerous from base (caudex), erect or ascending, unbranched, 0.5–2.5(–3.6) dm, (glabrous throughout or pubescent along proximal 1/2, trichomes simple).
petiole 0–1 cm;
blade spatulate, oblanceolate, oblong, or obovate, (0.4–)1–4(–5) cm × (3–)6–15(–20) mm, margins dentate to denticulate, apex obtuse or acute, surfaces usually pubescent, rarely subglabrate, trichomes stellate with simple rays.
petiole 0.3–2(–3.5) cm, (glabrous or ciliate);
blade narrowly oblanceolate, spatulate, to obovate, 0.4–2(–3) cm × 3–10(–15) mm, margins entire, (ciliate or not), apex obtuse, surfaces glabrous or sparsely to densely pubescent, trichomes simple, rarely mixed with forked ones.
3–5(–6);
blade oblong or ovate, 1–3 cm × 5–15 mm, base subcordate or auriculate, margins usually dentate, rarely subentire, apex acute or obtuse.
(1 or) 2–5(–7);
blade linear, oblanceolate, oblong, or obovate, 0.5–2.2(–3) cm × 2–8(–12) mm, base not auriculate, margins entire, (sometimes ciliate), apex obtuse, surfaces glabrous or, rarely, sparsely pubescent.
simple, (lax).
simple, (dense or lax).
sepals oblong, 2.5–4(–4.7) × 1–2 mm, lateral pair conspicuously saccate basally;
petals white, spatulate to obovate, 5–8(–9) × 2–3.5 mm, apex obtuse;
filaments 3–5 mm;
anthers oblong, 0.7–1.2 mm.
sepals (greenish) oblong, 2.5–3.5 × 1.2–1.5 mm, lateral pair saccate basally, (glabrous);
petals white, oblanceolate to spatulate, (5–)6–8 × 2–4 mm, apex rounded;
filaments 2.5–4 mm;
anthers oblong, 0.6–1 mm.
ascending to divaricate, 4–10(–12) mm.
ascending to divaricate, (2–)5–20(–30) mm, (glabrous).
ascending to spreading, torulose, 1.7–3.5(–4) cm × 1–1.7 mm;
valves each with midvein absent or obscure, along proximal 1/2;
ovules 34–50 per ovary;
style 0.3–0.6 mm.
ascending to suberect, (not appressed to rachis), slightly torulose, sometimes slightly curved, (0.7–)1–2.5(–2.8) cm × 0.8–1.2(–1.5) mm;
valves each with distinct midvein extending full length;
ovules 10–24 per ovary;
style 0.5–1.2(–2) mm, (slender).
narrowly winged throughout, ovate, 1–1.4 × 0.9–1.1 mm;
wing 0.1–0.2 mm wide.
not winged, broadly ovate, 0.6–1.2(–1.5) × 0.5–1 mm.
= 16.
= 32.
Arabis alpina
Arabis nuttallii
Arabis alpina, the generic type, is variable. It is cultivated extensively for its attractive flowers, and it sometimes escapes from cultivation. There is disagreement as to whether one or more species should be recognized in this complex. European, some African, and most North American plants are recognized as A. alpina; most of the larger-flowered, southwestern Asian plants, which are most commonly cultivated, are recognized as A. caucasica or as A. alpina subsp. caucasica (Willdenow) Briquet. In my opinion, the morphological differences between the two (see key, couplet 3) support recognition of two species, as did R. C. Rollins (1993) and G. A. Mulligan (1996).
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Arabis nuttallii, the second most widespread native North American species of the genus, is variable in density of indumentum, types of trichomes, plant height, pedicel length, fruit width, leaf shape, flowering and fruiting time, and elevation. As indicated by R. C. Rollins (1941, 1993), the variation seems to be sporadic and does not correlate with clear-cut entities and, therefore, the species cannot be subdivided meaningfully.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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