Astragalus tridactylicus
Proc. Amer. Acad. Arts 6: 527. 1865.
Plants cespitose, mat- or cushion-forming, (0.5–)1–4 dm wide, acaulescent or subacaulescent, 0–1.5 cm, silvery-pilose; taproot stout; from branched caudex, branches with thatch of persistent petioles and stipules. Stems obscured by stipules. Leaves 0.5–6(–6.5) cm; stipules 5–10 mm, hyaline, proximally pilose abaxially; leaflet blades spatulate to narrowly lanceolate, 2–20 mm, apex acute, surfaces silvery-pilose. Peduncles 0–1 cm. Racemes 2–6(–10)-flowered; axis very short; bracts 1.5–5 mm; bracteoles 0. Pedicels 1–3.5 mm. Flowers 8.2–11.5 mm; calyx campanulate to turbinate-campanulate, 4.5–6.9 mm, densely silvery-pilose, tube 1.8–3.5(–3.8) mm, lobes lanceolate-subulate, 1.8–3.5 mm; corolla usually pink-purple, rarely white; banner recurved through 90°; keel 4.4–7.2 mm, apex obtuse. Legumes ascending, ovoid-ellipsoid, slightly compressed, 4–5 × 1.2–2 mm, papery, densely silky-strigose or silky-pilose. Seeds 6–12.
Phenology: Flowering late May–Jul.
Habitat: Bluffs and knolls on rolling plains, on sand or gravelly clay, shale, sandstone, or limestone, especially on red sand of the Chugwater Formation.
Elevation: 1400–2300 m.
Discussion
Astragalus tridactylicus occurs from near Denver, Colorado, northwestward to the Laramie Plains and northward to near Casper, Wyoming.
Selected References
None.