Slender, diffuse, with a subfiliform taproot, hirsutulous throughout with rather stiff, loosely ascending, straight or incurved hairs up to 0.6-0.8 (0.9) mm. long, the herbage greenish-cinereous, the leaflets equally pubescent on both sides or medially glabrescent above; stems 1—17 cm. long, the central one erect, not over 2.5 cm. long and somewhat inhibited, with very short internodes, the lateral ones 1—2 from the axils of the cotyledons, prostrate, simple or either spurred or branched at the first 1—2 nodes, composed of about 1—7 developed internodes up to 1.5-3.5 (4) cm. long; stipules deltoid or lance-triangular, 1-2.2 mm. long, the lowest papery-membranous, semi- or almost fully amplexicaul, the upper ones narrower, thinly herbaceous, thinly pubescent dorsally; leaves 1-4 cm. long, with 7-13 crowded, oblong-obovate, retuse, loosely folded leaflets 2-7 mm. long; peduncles 0.3—1.5 (2.5) cm. long, much shorter than the leaf; racemes loosely 1-4-flowered, the flowers early declined, the axis 0-1.5 cm. long in fruit; bracts membranous, triangular-acuminate, 0.6-1 mm. long; pedicels 0.8-1 mm. long, recurved and persistent in fruit; bracteoles 0; calyx 3—4 mm. long, white-hirsutulous, the symmetrically turbinate disc 0.6—0.7 mm. deep, the submembranous, purplish tube 1.6—2.3 mm. long, 1.3—1.7 mm. in diameter, the firmer, lance- subulate teeth 1.3—2 mm. long; petals whitish, the banner faintly lilac-veined; banner recurved through ± 40°, ovate- or obovate-cuneate, shallowly notched, 4.2—5.4 mm. long, 2—3 mm. wide; wings (3.5) 4—4.9 mm. long, the claws 1.7—2.2 mm., the narrowly oblong-oblanceolate, obtuse, slightly incurved blades (2) 2.5—3.5 mm. long, 0.8—1.3 mm. wide; keel 3.7—4.5 mm. long, the claws 1.8—2.2 mm., the half-obovate blades 1.6—2.5 mm. long, 1.1—1.4 mm. wide, abruptly incurved through 90-95° to the bluntly deltoid apex; anthers 0.25-0.3 mm. long; pod declined, linear-oblong in profile, incurved through ¼½ circle, 1.3-1.8 cm. long, 2.8—4.1 mm. in diameter, cuneate at base, tapering and cuspidate at apex, compressed-triquetrous with nearly flat lateral and narrower, sulcate dorsal faces, the thin, pale green valves becoming papery and stramineous or brownish, cross- reticulate, hirsutulous with ascending or incurved hairs up to 0.55-0.85 mm. long, inflexed as a complete septum 1.7-2 mm. wide; ovules 12-14; seeds subquadrate, brown sometimes speckled with purple, irregularly wrinkled, 1.9-2.5 mm. long.—Collections: 5 (i); representative: Eastwood & Howell 8966 (CAS); Train 1719 (NA).
Outwash fans and gravelly flats in the foothills of calcareous desert mountains, 2050-4500 feet, rare and local, known only from a few scattered localities in Clark (Las Vegas; Moapa; Indian Springs; Lee Canyon) and southern Nye (type-locality) Counties, Nevada.—Map No. 147.—April and May.
Astragalus nyensis (of Nye County, Nevada) Barneby in Leafl. West. Bot. 8: 195. 1954, based on A. Nuttallianus var. pilifer (hairy, of the loose, hirsutulous vesture) Barneby in op. cit. 3: 110, Pl. opp. p. 108. 1942 ("piliferus", an incorrect form).—"Nevada: ...foothills of the Spotted Range, Nye Co. ... Ripley & Barneby 3430"—Holotypus, collected May 14, 1941, CAS! isotypi, RSA, UC (Clokey)!
Three annual milk-vetches with slenderly oblong, trigonous fruits are known to occur under similar conditions in the Larrea and Joshua-tree deserts of southern Nevada. The commonest of them, A. Nuttallianus var. imperfectus, is easily distinguished from the endemic A. nyensis by its appressed vesture, prevailingly elliptic and acute (and never retuse) leaflets, and only minutely strigulose or glabrous, long-persistent pod more abruptly incurved just above the base than distally. The third species, A. acutirostris, is seemingly very rare in Nevada; it resembles A. nyensis in the retuse leaflets, but the acute keel-tip and commonly resupinate pods, carried out on much longer peduncles beyond the fulcrant leaf, provide firm differential characters at all stages of growth.
The Nye milk-vetch, despite its interest for the specialist, can lay no claim to prettiness. When in full flower the tiny, whitish or dimly roseate corollas are almost concealed by foliage, and even the fruits, because of their short common peduncle and mask of spreading-incurved hairs, do not stand out from the leaves to a casual glance. Although certainly a rare plant, A. nyensis is easily overlooked and may prove more widely distributed than collections show to date.
The Nye milk-vetch was first collected in May, 1906, at Indian Springs in the east foothills of the Charleston Mountains, by M. E. Jones.