1. Arabis alpina Linnaeus, Sp. Pl. 2: 664. 1753.
Arabis alpina var. glabrata A. Blytt
Perennials; (stoloniferous, with vegetative rosettes, loosely cespitose to somewhat pulvi-nate); sparsely to moderately pubescent, trichomes stalked, cruciform, stellate, mixed with simple and forked-stalked ones. Stems usually simple from base, erect to ascending, often branched proximally, (0.6-) 1-2(-2.5) dm. Basal leaves: 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. Cauline leaves 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. Racemes simple, (lax). Fruiting pedicels ascending to divaricate, 4-10(-12) mm. Flowers: 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. Fruits 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. Seeds narrowly winged throughout, ovate, 1-1.4 × 0.9-1.1 mm; wing 0.1-0.2 mm wide. 2n = 16.
Flowering Jun-Aug. Crevices of limestone rocks, along streams, calcareous alpine meadows, Salix scrub on slopes with scree; 0-2400 m; Greenland; Nfld. and Labr., Nunavut, Que.; N.Y., Wash.; Europe; sw Asia; n, tropical Africa.
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).