318b. Astragalus mohavensis var. mohavensis
Calyx 4.9-7.2 mm. long, the tube 2.7-4.4 mm. long, 2.3-3.3 mm. in diameter, the teeth 1.8-2.8 mm. long; banner (8.8) 9-12.5 mm. long, 5.5-8 mm. wide; wings 7.8-10 mm. long, the claws 2.4-4.5 mm., the blades 5.4—6.5 mm. long, 2.1-2.6 mm. wide; keel (0.1 mm. longer to 0.4 mm. shorter than the wings) 7.5-9.6 mm. long, the claws 2.9-4.7 mm., the blades 4.9-5.8 mm. long, 2.6-3.4 mm. wide; pod as described in the key; seeds 2.6—3.5 mm. long. Collections: 24 (iv); representative: Ferris 7938 (CAS, NY, OB, WS); Munz 16,435 (CAS, POM); Coville & Funston 501 (NY); Clokey 7991 (NA, NY); Peebles & Loomis 165 (NY); Ripley & Barneby 2921, 3323 (RSA).
Dry rocky slopes and flats in the foothills of desert mountains, along boulder- strewn washes, and on rock ledges of canyon walls, mostly 2500-7500 feet, descending in Death Valley to 1200 feet, most common in the Larrea belt but ascending into the piñon-juniper forest, apparently more abundant on limestone but not exclusively calciphile, well distributed and locally plentiful in the northern Mohave Desert, from the Death Valley region in Inyo County, California, east to the Pintwater and Charleston Mountains in Clark County, Nevada, south, becoming rarer, to the north edge of the Colorado Desert in the Eagle Mountains and Pinto Basin, interior Riverside County, California.—Map No. 144.—April to June.
Astragalus mohavensis (of Mohave River) Wats. in Proc. Amer. Acad. 20: 361. 1885 ("Mohavensis").—"In a canon south of Newberry Spring in the Mohave Valley, in large depressed masses, by Mr. and Mrs. J. G. Lemmon, May, 1884."—Holotypus (Lemmon 3117, dated "April, 1884"), GH! isotypi, K, P!—Brachyphragma mohavense (Wats.) Rydb. in N. Amer. Fl. 24: 400. 1929.
The Mohave milk-vetch is well adapted to life under desert conditions, for although potentially perennial the plants are of rapid growth, in dry seasons flowering and beginning to fruit as month-old seedlings an inch or two in height, thereby ensuring the future of their sort. With ample moisture at the appropriate moments, the plants become much larger, but only rarely form the large masses described by Lemmon. Erect when young or short, the stems early become diffuse; when anchored in rock fissures, they hang down to form a silvery curtain of foliage against the canyon wall. The species may be recognized among other annual and short-lived milk-vetches of the Mohave by its few, broad, canescent leaflets, and by the plumply oblong-ellipsoid or sausage-shaped pod of solid, at first succulent, translucently green and lustrous aspect, which eventually shrinks into a hard, wrinkled, straw-colored shell girdled by the salient sutures. Because of the weight of water within the juicy mesocarp, the young pods are usually humistrate, or hang vertically from pendulous racemes and become technically erect in relation to the raceme-axis. Moreover their lack of angles permit them to roll or fall at random attitudes when laid into the press, and the naturally pendulous orientation is therefore often disguised in herbarium specimens. Variations in form and curvature of the pod, which is most often subsymmetrically oblong, is described in the varietal key. The flowers, though small, are of a lively pink-purple enhanced by a striate eye in the banner and, as seen in profile, have a characteristic blunt-ended look, due to the prominent keel which about equals the wings and is scarcely shorter than the banner.