Monographs Details: Astragalus didymocarpus Hook. & Arn. var. didymocarpus
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:

360a. Astragalus didymocarpus var. didymocarpus

Herbage green or greenish-cinereous, the vesture commonly sparse, appressed or nearly so, the leaflets glabrous or thinly pubescent near the margins above, stems characteristically erect or ascending, more rarely (especially in exceptionally dry or compact soils) diffuse and freely branched, (2.5) 4—35 (45) cm. long, leaves (0.8) 1.5-7.5 cm. long, the (9) 11-17 leaflets 1.5-14 mm. long; racemes (5) 7-25-flowered, at full anthesis 5-8 mm. in diameter, the axis 2-15 (22) mm. long in fruit; calyx 2.5—3.8 (4) mm. long, densely pilosulous with rather stiff, straight, spreading or loosely ascending, black and white or largely black hairs up to 0.5-0.8 mm. long, the tube 1.5-2.8 mm. long, 1.3-2 mm. in diameter, the subulate teeth 0.8-1.4 (2) mm. long; banner 2.8-5.3 (6.1) mm. long, 1.6-2.5 (3) mm. wide; wings 2.8-4.8 (5.2) mm. long, the claws 1.2-2.4 mm., the blades 1.8-3 (3.2) mm. long, (0.6) 0.8-1.2 mm. wide; keel 2.4-4.3 (4.5) mm. long, the claws 1.3-2.4 mm., the half-obovate blades 1.2-2.3 (2.6) mm. long, 0.8-1.2 (1.5) mm. wide, abruptly incurved through 90-95° to the blunt, deltoid apex; anthers 0.15-0.25 (0.3) mm. long; pod (2) 2.3-3.4 (4) mm. long, 1.5-3 mm. in diameter, strigulose throughout or in the distal half only, the hairs sometimes appearing loose on the corrugated angles.—Collections: 71 (iv); representative: Wiggins & Ferris 9360 (NY, TEX, WS); Raven 9220 (CAS, RSA); C. B. Wolf 6373 (CAS, TEX, WS), 6659 (CAS, WS), 10,295 (CAS, NY, TEX, WS); Jones 3152 (NY, POM, TEX); Palmer 614 (CAS, NY); Wiggins 5232, 5245 (CAS, NY).

Grassy hillsides, rolling plains, and valley floors, widespread and locally abundant below 2200 feet in the South Coast Ranges and adjacent Great Valley of California, from the lower Sacramento Valley in Contra Costa County southward in scattered stations near the coast to lat. 30° N. in Baja California, coming out to the Pacific Coast southward from Santa Barbara County and the Channel Islands (all but San Nicolas and Santa Barbara), extending rarely east into the Sierra foothills in Madera County, and ascending to 4400 (5080) feet in the mountains of Ventura County; also on sandy flats and stony washes, with Larrea and Joshua- tree, up to 3100 feet, in the southwestern and (rarely) central Mohave Desert; and apparently isolated at 3800-4400 feet on both slopes of the Funeral Range in southern Nye County, Nevada, and adjoining Inyo County, California.—Map No. 160.—March to May.

Astragalus didymocarpus (with pod divided into twin lobes) H. & A., Bot. Beechey Voy. 334, Pl. LXXXI. 1840.—"California, Douglas."—Holotypus, collected in 1833, K! isotypi, BM, G, K, NY, OXF!—Tragacantha didymocarpa (H. & A.) O. Kze., Rev. Gen. 944. 1891. Hesperastragalus didymocarpus (H. & A.) A. Heller, Muhlenbergia 2: 218. 1905.

Astragalus catalinensis (of Catalina Island) Nutt. in Jour. Acad. Philad. II, 1: 152. 1848.—"On the island of Catalina, in Upper California," collected by Dr. William Gambel.—Holotypus, labeled "A. Catalinensis Nuttall, from Gambel," K!—Hesperastragalus catalinensis (Nutt.) Rydb. in Bull. Torr. Club 53: 169. 1926.

Hesperastragalus compactus (dense, of the raceme) A. Heller, Muhlenbergia 2: 218. 1906.—"The type is no. 8156, collected April 11, 1906, on grassy hills near Pollaskey, Fresno County, California."—Isotypi (A. A. Heller 8156), GH, MO, NY, US!

? Astragalus didymocarpus var. daleoides (resembling some annual daleas in habit and calyx) Barneby in El Aliso 2: 212. 1950.—California: Cholame, San Luis Obispo Co., 5 May 1926, Eastwood 13875, in part; ibid, 25 March 1935, J. T. Howell 2026, in part... -Cotypi, CAS!

The prevailing form of the typical two-seeded milk-vetch, var. didymocarpus, is a slender plant with a solitary or several erect or ascending stems, green herbage with leaflets varying from oblong to linear (the latter commonest southward and on the Channel Islands), and capitate or narrowly oblong, black-hairy flower-heads about 5-8 mm. in diameter. A diffuse form, in which the short-toothed calyx of var. didymocarpus is combined with the diffuse growth-habit of var. dispermus, occurs in semidesert environment on the floor of the San Joaquin Valley (e.g., J. T. Howell 5870, CAS); and there is difficulty in distinguishing them where these two varieties converge in the western Mohave Desert. The occurrence of var. didymocarpus in characteristic form in the Death Valley region, somewhat doubtfully recorded earlier (Barneby, 1950, p. 212), has been confirmed by recent collections (e.g. J. & L. Roos 6086, NY). It is apparently established on both slopes of the Grapevine and Funeral Ranges, though whether truly native there is open to question. The pod of var. didymocarpus varies from rather densely hairy over the whole surface to glabrous proximally and thinly or sometimes only minutely strigulose at apex with white or sometimes a few black hairs. I agree with James (1951, p. 68) that H. compactus represents no more than a point on a fully documented scale of variation.

A notably unusual form of A. didymocarpus with deeply campanulate calyx and teeth up to 2 mm. long (more or less equaling the banner) was described as var. daleoides Barneby from specimens collected near Cholame and San Miguel in San Luis Obispo County. Both gatherings from Cholame were mixed with typical var. didymocarpus, and I have had growing doubts as to whether the proposition was entitled to more than passing notice as a minor variant. The name is listed here for the present as a doubtful synonym of var. didymocarpus, pending confirmation or rejection after study of more material.