Arabis alpina
Arabis pycnocarpa
alpine rockcress, arabis alpina
blushing rock-cress, cream-flower rock-cress, hairy eared-rockcress, hairy rockcress, slender rock cress
usually simple from base, erect to ascending, often branched proximally, (0.6–)1–2(–2.5) dm.
simple or several from base (rosette), erect, often branched distally, 1–8 dm, (pilose with trichomes appressed, malpighiaceous, or minutely stalked, forked, or hirsute basally with trichomes simple and minutely stalked, forked, sometimes almost exclusively pubescent with forked submalpighiaceous trichomes).
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 0.5–2 cm, (ciliate or not);
blade spatulate, oblanceolate, or oblong, (0.8–)1.5–8 cm × (5–)10–25 mm, margins entire, repand, or dentate, apex obtuse or acute, surfaces sparsely to densely pubescent, trichomes sessile or stalked, simple or forked, and/or stellate.
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.
(7–)10–45(–61), (overlapping or not);
blade ovate to oblong or lanceolate, rarely linear, (1–)1.5–6(–8) cm × (1–)3–20(–25) mm, base subcordate or auriculate (auricles obtuse or subacute), margins dentate or entire, apex acute or obtuse, surfaces hirsute or adaxially glabrescent.
simple, (lax).
often simple.
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 oblong, 2.5–4 × 0.5–1.5 mm, lateral pair not saccate basally;
petals white, linear-oblanceolate or narrowly spatulate, 3.5–5(–5.5) × 1–2(–2.5) mm, apex obtuse;
filaments 2.5–4 mm;
anthers oblong, 0.7–1 mm.
ascending to divaricate, 4–10(–12) mm.
erect to erect-ascending, (2–)3–8(–12) mm (glabrous or sparsely pubescent).
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.
erect to erect-ascending, (often appressed to rachis), torulose, (3.5–)4–6(–6.5) cm × 0.8–1(–1.2) mm;
valves each with obscure or somewhat prominent midvein extending to the middle;
ovules (54–)60–86 per ovary;
style (0.2–)0.5–1(–1.3) mm, (slender).
narrowly winged throughout, ovate, 1–1.4 × 0.9–1.1 mm;
wing 0.1–0.2 mm wide.
narrowly winged throughout, oblong or suborbicular, (0.8–)1–1.5(–1.7) × 0.8–1.3 mm;
wing to 0.2 mm wide distally.
= 16.
Arabis alpina
Arabis pycnocarpa
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.)
Varieties 2 (2 in the flora).
M. Hopkins (1937) synthesized earlier works on Arabis pycnocarpa and concluded that it is different from the European A. hirsuta. Both R. C. Rollins (1941, 1993) and G. A. Mulligan (1996) considered the North American and European plants different varieties of A. hirsuta; Mulligan recognized var. hirsuta in North America and Rollins did not. After examining thousands of specimens from Europe, Asia, and North America, I conclude that Hopkins was correct in treating the North American plants as a different species, A. pycnocarpa. The European A. hirsuta is a diploid (2n = 16) that has fruits 1.5–4 cm, stout styles 0.1–0.5 mm, prominent midvein extending the full length of the fruit valve, and 30–40(–44) ovules/seeds per ovary/fruit. By contrast, A. pycnocarpa is a tetraploid (2n = 32) that has fruits (3.5–)4–6(–6.5) cm, often slender styles (0.2–)0.5–1(–1.3) mm, obscure midvein hardly extending to the middle of the fruit valve, and ovules/seeds (54–)60–86 per ovary/fruit. Hopkins listed other differences in the number of cauline leaves and the development of seed wing, but these do not hold. Mulligan treated the perennial North American plants with minute styles as var. hirsuta and the biennial ones with longer styles as var. pycnocarpa. Habit and style length are not correlated at all, and one finds both biennials and perennials flowering in the same population.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
1. Stems usually hirsute basally, rarely glabrescent, trichomes often simple, sometimes branched; basal leaf blades: surfaces with simple and stalked trichomes. | var. pycnocarpa |
1. Stems pilose, trichomes appressed, malpighiaceous, or minutely stalked, forked; basal leaf blades: surfaces with sessile, forked, and/or stellatetrichomes. | var. adpressipilis |
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