Monographs Details: Astragalus lentiformis A.Gray
Authors:Rupert C. Barneby
Authority: Barneby, Rupert C. 1964. Atlas of North American Astragalus. Mem. New York Bot. Gard. 13(2): 597-1188.
Family:Fabaceae
Discussion:

350.  Astragalus lentiformis

Low, slender, with a thick, woody taproot and shortly forking, suffruticulose caudex, gray-villosulous with fine, spreading, partly sinuous or twisted hairs up to 0.5-1 mm. long, the stramineous stems thinly so, the herbage greenish-cinereous, the leaflets glabrescent above; stems many, diffuse, simple above the immediate base, 9-18 cm. long; stipules up to 7 mm. long, the lowest membranous, pallid, strongly adnate and also connate into a loose, bidentate sheath, the upper ones firmer or herbaceous, broadly lanceolate to linear-acuminate, semi- or almost fully amplexicaul, free; leaves 1.2-3.5 cm. long, the uppermost shortly petioled or subsessile, with 7-15 oblanceolate, narrowly obovate, or elliptic, obtuse or subacute, dorsally keeled, loosely folded leaflets 2-10 mm. long; peduncles slender, incurved- ascending, 4-16 mm. long, shorter than the leaf; racemes shortly but loosely 5-10-flowered, the flowers early declined, the axis 4-16 mm. long in fruit; bracts membranous or membranous-margined, linear or linear-lanceolate, 1.5-3 mm. long; pedicels slender, 1-1.8 mm. long, in fruit little elongated or thickened, recurved or reflexed, tardily disjointing; bracteoles 0; calyx 3.6-4.5 mm. long, white-villosulous, the slightly oblique disc 0.5-0.6 mm. deep, the tube 2.2-2.9 mm. long, ±2 mm. in diameter, the subulate teeth 1.3-2.3 mm. long, the whole becoming papery, ruptured, marcescent; petals at first ivory-yellow, drying deeper yellow, the banner faintly brown-veined when dry; banner recurved through ± 50°, ovate-cuneate, notched, 6.2-7 mm. long, 3.8-4.5 mm. wide; wings 6-6.6 mm. long, the claws 2.2-2.6 mm., the lance-elliptic blades 4-4.2 mm. long, 1.5-1.7 mm. wide, both incurved but the left one more abruptly so and infolded over the keel; keel 4-4.9 mm. long, the claws 2-2.5 mm., the half-circular blades 2.3-2.5 mm. long, 1.4-1.7 mm. wide, abruptly incurved through 130° to the deltoid, obscurely porrect apex; anthers 0.3-0.4 mm. long; pod declined, sessile, tardily deciduous, symmetrically or subsymmetrically oblong-lenticular in profile, 5-8.5 mm. long, 2.5-3 mm. in diameter, rounded at base, contracted at apex into a subulate cusp ±1 mm. long, laterally compressed-triquetrous, with almost flat lateral faces much broader than the depressed but scarcely sulcate dorsal one, carinate ventrally by the prominent but slender suture, the thin, pale green valves villosulous with ascending or incurved-ascending hairs, becoming stramineous, papery, reticulate, inflexed as a complete septum 1.5—2 mm. wide; dehiscence apical, basal, and through the ventral suture; ovules 6—10; seeds brown, smooth, somewhat lustrous, ± 2 mm. long.—Collections: 6 (o); representative: Lemmon 50 (G, NY), 73 (CAS, MO, NY); Eastwood 7021 (CAS, UC, US); /. T. Howell 37,702 (NY).

Dry sandy soil among sagebrush, sometimes with Jeffrey pine, 4800—5100 feet, rare and local, known only from Sierra and Clover \ alleys, at the east foot of the northern Sierra Nevada, in Plumas and Sierra Counties, California. Map No. 158.—May to July.

Astragalus lentiformis (lentil-shaped, of the pod) Gray ap. Brew. & Wats., Bot. Calif. 156. 1876.—"Sierra Nevada, in Clover Valley, &c., on the borders of California and N.W. Nevada, Lemmon"—Holotypus, Lemmon 537 in 1874, GH! isotypus, UC!—Tragacantha lentiformis (Gray) O. Kze., Rev. Gen. 946. 1891.

The lentil milk-vetch is an inconspicuous plant, notable principally for its rarity and for the small size of all its parts. Only two other astragali with flowers as small are known to occur in the Sierra Valley region; both are easily distinguished from A. lentiformis, the related A. Lemmoni by its appressed vesture, free stipules, and paired peduncles, and the apparently more distantly akin even though habitally similar A. Pulsiferae by its inflated, unilocular fruit. The combination in the lentil milk-vetch of the growth-habit and pubescence of A. Pulsiferae var. Suksdorfii with the pod, scarcely altered, of A. Lemmoni, suggests that the species may have arisen through hybridization between these sympatric, even though ecologically disparate, small- flowered astragali.

Specimens of A. lentiformis were distributed by Lemmon under at least four serial numbers, without indication of exact locality, so that I cannot tell whether he collected it in more than two stations, the Clover and Sierra Valleys of the original description. It was rediscovered by Alice Eastwood near Portola in Plumas County and collected in the same place as lately as 1962 by John Thomas Howell. The colony discovered by Mr. Howell consisted of only three plants.