Montana Field Guide

Perennial often forming loose mats from a branched caudex. Herbage glabrate to densely strigillose. Stems prostrate to ascending, 5–30 cm. Leaves with 7 to 11 linear-lanceolate to narrowly elliptic leaflets, glabrate above, 5–12 mm long with acute tips; stipules lanceolate, 2–4 mm long, basally connate. Inflorescence ca. as long as the leaves, with 5 to 10 spreading flowers. Flowers white to purple; calyx black- and/or white-strigose; sepals 1–2 mm long; banner 6–8 mm long, erect; keel 3–6 mm long, purple-tipped. Legume spreading, narrowly ovate, white-strigillose, 6–13 mm long, flattened but swollen around the seeds (Lesica et al. 2012. Manual of Montana Vascular Plants. BRIT Press. Fort Worth, TX).

Compact and pulvinate forms are similar to Astragalus kentrophyta, which differs in having stiffly pungent leaflets that are continuous with, not jointed, to the leaf rachis. The narrowly endemic A. vexilliflexus var. nubilus of central Idaho differs in being (sub)alpine, consistently compact and low to the ground, and in having loosely silky-villous hairs. This form should be sought in SW Montana.

POLLINATORS
The following animal species have been reported as pollinators of this plant species or its genus where their geographic ranges overlap: Bombus vagans, Bombus appositus, Bombus auricomus, Bombus bifarius, Bombus borealis, Bombus centralis, Bombus fervidus, Bombus flavifrons, Bombus huntii, Bombus mixtus, Bombus nevadensis, Bombus rufocinctus, Bombus ternarius, Bombus terricola, Bombus occidentalis, Bombus pensylvanicus, Bombus griseocollis, and Bombus insularis (Macior 1974, Thorp et al. 1983, Mayer et al. 2000, Colla and Dumesh 2010, Wilson et al. 2010, Koch et al. 2012, Miller-Struttmann and Galen 2014, Williams et al. 2014).