Astragalus magdalenae var. niveus

Herbage silvery-cinereous, the longest hairs ascending, up to 0.55-0.75 mm. long; leaflets as in var. magdalenae but commonly less crowded; calyx 5-6.2 mm. long, the tube 3-3.8 mm., the teeth 1.8-2.5 mm. long; keel 8.2-9.7 mm. long; pod obliquely ellipsoid or half-ellipsoid, 1-2 cm. long, 6-11 mm. in diameter, the beak ± 2-3 mm. long.—Collections: 6 (o); representative: Bacigalupi 2872 (CAS, DS, SMU); Raven 11,642A (NY); Dressier 595a (MO); Johnston 3306 (CAS, K, US).

Dunes and sandy flats behind the beaches, below 40 feet, known from scattered stations around the head of the Gulf of California (San Felipe Bay, Baja California; Adair and Tepoca Bays, northwestern Sonora); and from the Pacific Coast near 29° 30' N.—Map No. 117.—February to April.

Astragalus magdalenae var. niveus (Rydb.) Barneby in Aliso 4: 135. 1958, based on Phaca nivea (snow-white) Rydb. in N. Amer. Fl. 24: 328. 1929. Type collected 15 miles north of San Felipe Bay, Lower California, February, 1904, MacDougal... "—Holotypus, collected by D. T. MacDougal, NY!—A. niveus (Rydb.) Barneby in Leafl. West. Bot. 4: 55. 1944.

The var. niveus is closely similar to var. magdalenae, but the somewhat longer and less tightly appressed vesture, less crowded and commonly slightly larger leaflets, slightly longer and paler flowers, and smaller pods containing fewer ovules and fewer but larger seeds provide the rather insecure basis for separating the two. At anthesis the plants of var. niveus resemble var. Peirsonii in everything except the more numerous lateral and jointed terminal leaflets and in the ordinarily longer peduncles, of which at least the more vigorous surpass the subtending leaf. The much larger pod and seeds of var. Peirsonii are distinctive later on. Like var. magdalenae, the present form of the satiny milk-vetch is known only from coastal dunes, but it may extend somewhat inland into the sandy wastes around the Colorado delta. In this area it may overlap the range of the similarly white-silky A. lentiginosus var. borreganus, an astragalus to be recognized by its very loosely or remotely racemose, larger, bright purple flowers and later by a lunately lanceolate, fully bilocular pod.