Astragalus osterhoutii
Plants stout, clump-forming, 25–45 cm, very sparsely strigulose; from shallow, subterranean caudex. Stems erect or ascending, very sparsely strigulose. Leaves sometimes unifoliolate distally, 3–8.5 cm; stipules shortly connate-sheathing and scarious at proximal nodes, connate or distinct and herbaceous at distal nodes, 2–8 mm; leaflets (1 or)5–15, blades linear-oblong, oblanceolate, or filiform, 6–40 mm, apex obtuse to acute, surfaces glabrous or sparsely strigulose abaxially, glabrous adaxially; terminal leaflet decurrent, not jointed to rachis. Peduncles erect, (6–)8–14 cm. Racemes 12–25-flowered, flowers spreading-declined; axis 2.5–10 cm in fruit; bracts 1–3.5 mm; bracteoles 1 or 2. Pedicels 2–6 mm. Flowers 17–23 mm; calyx 8.5–12 mm, strigulose, tube 7–10 × 3.5–4.7 mm, lobes triangular-subulate, 0.8–2 mm; corolla white; keel 12.3–14.8 mm. Legumes pendulous, green-stramineous, straight or slightly incurved, linear-ellipsoid, strongly laterally compressed, 25–45 × 3–4 mm, fleshy becoming stiffly papery, glabrous; stipe 2–6.5 mm. Seeds 12–17.
Phenology: Flowering Jun–Aug.
Habitat: Seleniferous clay hills, barren knolls, bluffs on openings in sagebrush-grass communities, under sagebrush.
Elevation: 2200–2400 m.
Discussion
Astragalus osterhoutii, with the combination of white flowers and stipitate, laterally compressed, ultimately deflexed and proportionally very long fruits, is unique in sect. Pectinati. This selenophyte, restricted to Grand County, was estimated to have a geographic range of approximately 120 km2 in soils derived from shales of the Niobrara, Pierre, and Troublesome formations (S. Spackman et al. 1997b). J. D. Karron (1989) reported this species as self-compatible, but not particularly autogamous. It was reported to have restricted genetic polymorphism, but still to exhibit a moderate level of isozyme variation (Karron et al. 1988).
Astragalus osterhoutii is in the Center for Plant Conservation’s National Collection of Endangered Plants.
Selected References
None.