Astragalus sterilis

  • Title

    Astragalus sterilis

  • Authors

    Rupert C. Barneby

  • Scientific Name

    Astragalus sterilis Barneby

  • Description

    88. Astragalus sterilis

    Dwarf, sparsely leafy, wiry, somewhat junceous, strigulose nearly throughout with straight, appressed or narrowly ascending hairs up to 0.35-0.5 mm. long, pale green or subcinereous; stems 6-16 cm. long, slender, simple, subterranean for a space of 2-8 cm., at emergence stouter and immediately branching, the short emersed internodes abruptly zigzag, each stem or small group of stems forming low entangled tufts; stipules 1.5-4 (5) mm. long, the buried and lowest aerial pairs papery-membranous, connate into a campanulate, bidentate sheath, the median and upper ones progressively smaller and more shortly connate or almost free, with deltoid or triangular-acuminate, mostly deflexed, herbaceous blades; leaves 2—9 cm. long, shortly petioled, with stiff rachis and 6—10 distant, often scattered, linear-elliptic, obtuse, involute, obscurely jointed leaflets 1-5 mm. long, the terminal one represented by a slight dilation of the rachis; peduncles slender, erect and incurved-ascending, (1) 2-7 cm. long; racemes very loosely (1) 2-5-flowered, the flowers early spreading, then declined, the axis (0) 1-6 cm. long in fruit; bracts membranous, ovate or subulate, 0.7-1.3 mm. long; pedicels at anthesis straight, ascending, 1-1.3 mm. long, in fruit arcuate-recurved, 1.5-2 mm. long; bracteoles 0; calyx 3.5-4 mm. long, thinly strigulose with white and a few black hairs, the subsymmetric disc 0.6-0.8 mm. deep, the pallidly submembranous tube 3-3.6 mm. long, 2.2-2.5 mm. in diameter, the deltoid or triangular-subulate, herbaceous teeth 0.4-0.6 mm. long, the whole becoming papery, marcescent unruptured; petals ochroleucous fading yellowish, concolorous; banner abruptly recurved through ± 85°, suborbicular-cuneate, shallowly notched, 9-10 mm. long, 6.5-8 mm. wide; wings 7.5-9.2 mm. long, the claws 3.5-4.5 mm., the oblong, obtuse, slightly incurved blades 5-5.4 mm. long, 1.8-2.2 mm. wide; keel 8-9 mm. long, the claws 3.7-4.2 mm., the broadly lunate blades 4.8-5 mm. long, 2.5-3 mm. wide, abruptly incurved through 85-95° to the triangular, sometimes subporrect, obtuse but beaklike apex; anthers 0.5-0.55 mm. long; pod pendulous, stipitate, the straight, slender stipe ± 3 mm. long, the obliquely obovoid body bladdery-inflated,  2-2.5 cm. long, 9-11 (when pressed up to 14) mm. in diameter, cuneately tapering at base into the stipe, abruptly contracted distally into a short and obscure, laterally compressed beak, otherwise a trifle dorsiventrally compressed, shallowly and openly sulcate ventrally, the filiform sutures both convexly arched but the dorsal one a little more strongly so, the papery-membranous, diaphanous, finely reticulate, glabrous valves purple-mottled on a pale green at length stramineous and lustrous ground, not inflexed; ovules 17—20; seeds (not quite ripe) ± 2—2.5 mm. long.—Collections: 3 (ii); representative: Ripley & Barneby 6149 (K, RSA); Peck 20,620 (WILLU, in bud only).

    Dry gravelly and sandy clay bluffs and knolls almost bare of other vegetation, in soils of basaltic origin, 4200-4300 feet, rare and local, known only from upper Sucker Creek in northwestern Owyhee County, Idaho, and from bluffs along the Owyhee River in adjoining Malheur County, Oregon.—Map No. 33.—June and July.

    Astragalus sterilis (barren) Barneby in Leafl. West. Bot. 5: 193. 1949.—"Idaho:... 24 miles southwest of Marsing, Owyhee County, alt. 4300 ft., 26 June, 1948, fl. & fr., Ripley & Barneby 9415."—Holotypus, CAS! isotypi, GH, IDS, NY, POM, RSA, US, UTC, WILLU.

    The barren milk-vetch, so called because of its shyness in bearing flowers and fruits even in favorable seasons, was first taken for a starveling form of A. Cusickii, but the root- system of the two species is so different that there can be no doubt we are dealing with two perfectly discrete entities. The main range of A. Cusickii lies farther north in the canyons of the Snake River, but it has been traced south to a point on Sucker Creek only a few miles distant from the small area near Rockville to which A. sterilis is apparently endemic. It seems possible that the latter arose as a favored mutation from A. Cusickii which developed a subterranean, eventually rhizome-like caudex and coincidentally became adapted to the specialized environment of open clay knolls or hilltops. The flowers and pods of the two species are closely similar, but A. sterilis is recognized at sight by its low, freely branching growth and few-flowered racemes.