Description
A perennial herb with a branching root-crown elevated upon a woody foot, each branch terminated by a tuft of very narrow (linear to linear-oblanceolate), untoothed leaves; stems several to many, 1.5-3 dm tall; pubescence grayish, finely dendritic hairs covering the leaves and lower stems; stem leaves sessile, generally broader than the basal, nonauriculate; flowers appearing May-June; petals purple, 7-8 mm wide; fruiting pedicels gently recurved; fruits pendulous, straight, 3-5 cm long, 1.5-2 mm wide, pubescent or rarely glabrous. The species name lasiocarpa refers to refers to the fruits which are usually (but not always) noticeably hairy.
Diagnostic Characteristics
Lacks auriculate cauline leaves, differentiating it from A. lemmonii which typically has at least some auriculate cauline leaves (Welsh et al. 2008). Rollins (1981) states that it differs from A. lignifera in having (1) more strongly recurved pedicels, (2) a many-branched, elongated caudex instead of one that is simple or few-branched, (3) relatively short, numerous stems rather than one or two stems, (4) usually pubescent instead of glabrous siliques, and (5) narrow and acuminate (rather than oblanceolate and obtuse) basal leaves. Windham and Al-Shehbaz (2006) argue that Arabis (Boechera) lasiocarpa in the strict sense differs from their newly-described Boechera rollinsiorum in its non-ciliate (vs. ciliate) petioles, non-auriculate (vs. auriculate) cauline leaves, and adaxial leaf surfaces and stems with 4- to 8-rayed trichomes 0.05-0.15 mm long (vs. 2- to 4(-5)-rayed trichomes 0.15-0.40 mm long). Fruits (siliques) of lasiocarpa are also often pubescent (can be both glabrous and pubescent in the same population), while young fruits of rollinsiorum are glabrous. Overall, Rollins (1993) stated that Arabis lasiocarpa "is distinguished by its intricately branched aerial caudex with each branch terminated by a tuft of erect linear to linear-oblanceolate entire leaves; the pubescence on the leaves and lower stems is of fine dendritic trichomes, the cauline leaves are small and far apart, and the usually pubescent siliques hang loosely from recurved, but not geniculately reflexed, pedicels."
Habitat
Lower montane to subalpine, growing in rock crevices and in rocky to gravelly soils of varying lithology (metamorphosed igneous chip-rock, whitish sedimentary rocks, quartzite sands, schist, limestone), in settings such as steep rocky hillside on various exposures. Sites occur within sagebrush, mountain brush, aspen, and spruce-fir communities. 1830 - 2930 m.