tusely triquetrous with rounded-convex ventro-lateral faces and deeply sulcate dorsal face, the thinly fleshy, green valves becoming stiffly papery, smooth or nearly so beneath the vesture, inflexed as a complete septum (0.9) 1.2-2.1 mm. wide, the septum produced upward at least into the base of the beak; dehiscence tardy, the pod falling entire but finally splitting through both sutures and the septum into two false carpels; ovules commonly 4, rarely 2, 3, or 6; seeds mahogany- or sooty-brown, elaborately pitted and wrinkled, 2.5—3.4 mm. long.—Collections: 30 (iii); representative: Eastwood 3164, 11,355 (CAS); Abrams 14,331 (NY, WS); /. T. Howell 1303 (CAS, NY), 18,018 (CAS, RSA, TEX), 29,146 (CAS, NY); Hoover 4038, 4920 (NY)\ Barneby 11,577 (CAS, NY, RSA).
Grassy flats, meadows moist in spring, and open slopes in the chaparral belt below 2000 feet, commonly on or near volcanic or serpentine outcrops, locally plentiful in propitious seasons in the interior valleys and foothills of the Coast Ranges in southeastern Mendocino, Lake, Napa, and Sonoma Counties, southwest to the Pacific slope of Mt. Tamalpais, Marin County, California.—Map No. 148. —Late March to June.
Astragalus Breweri (William Henry Brewer, 1828-1910, principal botanist of the California Geological Survey, 1860-1864, author with Sereno Watson of the first state flora) Gray in Proc. Amer. Acad. 6: 207. 1864.—"California, ‘in the Sonoma valley, common in fields: April 18.’ Dr. W. H. Brewer."—Holotypus (Brewer 979), GH! isotypi, K, NY, UC, US! —Tragacantha Breweri (Gray) O. Kze., Rev. 943. 1891.
Over a small part of its range in Lake and Mendocino Counties A. Breweri is sympatric with forms of A. Rattani. The two species, found in similar environments, are much alike in habit of growth and floral morphology. Flowering specimens of the Brewer milk-vetch may be distinguished by the few ovules, usually four or very rarely up to six as opposed to eight or more in A. Rattani; but the extremely distinct fruits form early in the season and provide the simplest means of identification. The remarkable fruits of the Brewer milk-vetch, which are disposed at the tip of the peduncles in a seemingly umbellate, stellately spreading or ascending cluster, are divided abruptly into two parts, an ovoid or oblong-ellipsoid body densely beset with silvery hairs, and an erect or slightly declined, long-subulate, almost spinelike beak of nearly equal length but much less densely pubescent. Comparison of the beak with that of A. Rattani shows the two to be of the same structure. And it is not difficult to imagine a mutation involving an abrupt shortening (or telescoping) of the pod-body in a precursor of both species, and consequently the elimination of the sterile base, which might produce a fruit of the A. Breweri type. A shortening of the fruit without loss of hairs might even produce the very striking inequality in density of pubescence between the body and the presumably unaltered beak. Such hypothesis is at least more plausible than that adumbrated by Rydberg when he created for A. Breweri a monotypic section in Astragalus (genuine) remote from its obviously close Californian allies in Hamosa sect. Leptocarpae. Likewise I can see no close connection between A. Breweri and the species with which Jones (1923, p. 284, the fig. on PL 71 very poor) associated it in sect. Didymocarpi.