Plants shortly caulescent (above­ground), 2–10 cm, strigulose; from deeply subterranean, often soboliferous, caudex. Stems prostrate to ascending and radi­ating, (0.5–)2–18(–24) cm under­ground, frequently exceeding aerial stem length, strigulose. Leaves 1–5.5 cm; stipules dis­tinct throughout or shortly connate-sheathing at prox­imal nodes, 2–5 mm, subherbaceous; leaflets closely spaced on rachis, blades obovate to elliptic or oblong, 1–12 mm, apex obtuse to retuse, surfaces gray-strigulose, sometimes glabrous adaxially. Peduncles ascending, 0.5–4 cm. Racemes (1 or)2–10-flowered; axis 0.3–1 cm in fruit; bracts 1.5–2.5 mm; bracteoles 0. Pedicels 1.2–3 mm. Flowers 9–17 mm; calyx 4.8–10.5 mm, strig­ulose, tube 3.5–7.6 mm, lobes subulate, 1.2–3 mm; corolla white or ochroleucous, or banner and wings tinged lavender, keel tip pink or purplish; keel 7.4–13.2 mm. Legumes pale green and red-cheeked, 15–38 × 8–23 mm, thin becoming papery, strigose; gynophore 1–4.5 mm.

Phenology: Flowering May–Jun.
Habitat: Barrens, often with other mound-forming species in mixed desert shrub, pinyon-juniper, mountain brush, and limber pine-Douglas-fir communities, on outcrops of the Green River Shale Formation.
Elevation: 1500–2900 m.

Distribution

• Generated Map
• Legacy Map

Colo., Utah.

Discussion

Astragalus lutosus, a highly specialized endemic to shale knolls and ridgetops almost bare of other plants, has its distribution aligned along, and within, a few miles of the fortieth parallel in northwestern Colorado and northeastern Utah. R. C. Barneby (1964) noted that it is one of the rarest of North American astragali.

Astragalus lutosus is in the Center for Plant Conservation’s National Collection of Endangered Plants.

Selected References

None.

Lower Taxa

None.