Description
A tufted perennial herb 1-3 dm tall, with a deep taproot continuing to a branching crown that is densely covered with old leaf bases, each crown topped with a stiffly erect cluster of lance-shaped leaves 2-5 cm long x 3-5 mm wide. The leaf blade tapers gradually into the petiole and is hairless except for a few hairs along the margin. There are only 3-5 stem leaves and these are linear, hairless, and 1-2 cm long x 1.5-3 mm wide. The flowering stem bears white flowers with spatula-shaped petals 3.5-4.5 mm long x 1.5 mm wide; the purplish sepals are about 2 mm long. Individual flower stalks are smooth and 3-8 mm long. The fruits (capsules) are borne in erect fashion and are linear-oblong and tapering at both ends, and only slightly flattened. At maturity they are purplish and 5-12 mm long x 1-1.5 mm wide. The seeds are brown, wingless, and about 2 mm long x 1 mm wide (Mozingo and Williams 1980, Rollins 1993).
Diagnostic Characteristics
Holmgren (2004) notes that Nevada (formerly Smelowskia) holmgrenii stands out from the seemingly similar genera Smelowskia, Braya, and Eutrema by its diploid chromosome number of 2n =14 and its unusual minute, rigid, broad-based, sharp-pointed, marginal hairs on the stiff basal leaves. It may also be related to the genus Polyctenium, but Polyctenium species differ from N. holmgrenii in having forked and branched hairs, leaves all cauline and deeply pinnatisect with narrow divisions, ovaries often containing 12 - 40 ovules (as opposed to fewer than 12), and a very different habitat type (lowlands, usually in silty, seasonally flooded soil) (Holmgren 2004), The stiff, erect and hairless leaves and capsules which are not flattened separate this species from superficially similar species of Arabis and Draba; it is also separated from Draba by its narrow, long capsules as opposed to capsule three times or less longer than wide in Draba (Mozingo and Williams 1980).
Habitat
This species occurs in cracks, cevices, ledges, rubble, talus, or small soil pockets on rock outcrops and cliffs, from high-elevation ridges to northfacing walls at lower elevations, on various rock types (e.g. calcareous rock, schist, metamorphic rock, igneous rock). Sites are found in the lower alpine, subalpine conifer, mountain sagebrush, and upper pinyon-juniper zones. Associated species include Heuchera rubescens, Leucopoa kingii, Holodiscus dumosus, Senecio canus, Mertensia oblongifolia, Erigeron compositus, Ribes cereum, and Selaginella watsonii. It occurs at elevations of 1,980 to 3,500 m.