Monographs Details: Astragalus argophyllus Nutt. var. argophyllus
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
Synonyms:Xylophacos argophyllus (Nutt.) Rydb., Astragalus argophyllus var. typicus Barneby, Xylophacos uintensis (M.E.Jones) Rydb., Astragalus uintensis M.E.Jones
Description:Variety Description - Root and caudex stout, tough, heavy; hairs of the herbage either all appressed or mostly narrowly ascending, straight or nearly so, up to (0.75) 1-1.65 mm. long; stems almost 0 up to 1 (1.5) dm. long; leaves (1.5) 2.5-12 (15) cm. long, with (7) 9-21 commonly elliptic, rhombic-elliptic, or -ovate and acute, more rarely oval-oblanceolate and obtuse, usually distant but sometimes crowded leaflets (2) 4-15 mm. long; calyx 12.4-16.8 mm. long, the tube (9.4) 10-11.8 mm. long, 3.4-4.6 mm. in diameter, the teeth 2.4-5 (5.8) mm. long; wings 20.6-23.8 mm. long, the claws 11.6-14.2 mm., the blades 9.2-12.2 mm. long, 2.1-3.5 mm. wide; keel (17.3) 17.6-20.3 mm. long, the claws 11.6-14.2 mm., the blades 6.1-7.4 mm. long, 2.7-3.4 mm. wide; pod 1.5-2.5 cm. long, 7-12 mm. in diameter, strigulose-pilosulous with straight, appressed or subappressed hairs up to (0.35) 0.5-1 mm. long.

Distribution and Ecology - Alkaline and saline meadows, moist at least in spring, stream banks and lake shores, in stiff alluvial clays and loams, sometimes in damp crevices about hot springs, 4500—7650 feet, scattered but locally abundant, central and northwestern Nevada north and eastward across the Snake River Plains to the upper forks of the Salmon River in Idaho, extreme southwestern Montana, the upper Wind River, Wyoming, and the San Pitch River in central Utah. Map No. 79. May to July.

Discussion:The silver-leaved milk-vetch is one of the few astragali of the intermountain region and the only one with large, purple flowers and silvery-silky leaflets that is confined to moist heavy soils, where it is subject to competition with sod-forming grasses, sedges, and other relatively rank herbaceous growth. The plants spring into flower with the year’s first warm weather, along with Carex Douglasii and Dodecatheon radicatum, and at anthesis form handsome ground-hugging mats or low tufts of silvery foliage seated on an extremely tough, woody root. The root and caudex, difficult to collect, are seen seldom in herbarium specimens. As the season advances and the surrounding turf grows up into the hay of summer, the piants are hidden from ready view and the green, fleshy, humistrate ovaries ripen slowly, in concealment, into the straw-colored or ultimately blackish, readily deciduous pods. The leaf-rachis in var. argophyllus is comparatively slender and flaccid, the leaflets tending to be small, distant, and diamond-shaped. Dried material does little justice to the brilliance of the fresh flower which dries out rapidly from a lively pink-purple to a dull slate-blue, an effect attributed by Jones to the alkalinity of the drying papers. However the chemistry of the sap and pigment has still to be investigated.
Distribution:Nevada United States of America North America| Utah United States of America North America| Idaho United States of America North America| Montana United States of America North America| Wyoming United States of America North America|