Monographs Details: Astragalus amphioxys var. modestus Barneby
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
Description:Variety Description - Habit of var. amphioxys, but the flowers smaller; calyx-tube 6.1-9.3 mm. long, 2.3-3.3 mm. in diameter, the teeth 1.1-2.6 mm. long; banner 12.8-16 mm. long, 5.8—8 mm. wide; wings 12—15 mm. long, the claws 6—7.4 mm., the blades 6.7—8.5 mm. long, 1.9—2.5 mm. wide; keel 11—12.7 mm, long, the claws 6.2—7.5 mm., the blades 5.4—6.3 mm. long, 2.3—2.7 mm. wide; pod 3—4 cm. long, crescentic or incurved through ½-circle; ovules 44-58.

Distribution and Ecology - Dry gravelly hillsides, sometimes among sagebrush, on limestone or in cin- dery volcanic debris, 4200-4550 feet, local, forming uniform colonies within the range of var. amphioxys but known only from valleys affluent to the Colorado River from the north in Lincoln County, Nevada, and northern Mohave County, Arizona.—Map. No. 92.—March to May.

Discussion:If we follow tradition by maintaining a var. vespertinus to accommodate the large-flowered race of A. amphioxys endemic to the Colorado Basin, it seems illogical to overlook the opposite extreme in flower-size which is found in a limited area of southern Nevada and adjoining Arizona. Neither of these varieties differs consistently from var. amphioxys in any feature of the pod. While var. vespertinus is dispersed partly within and partly to the northeast of the typical variety, the range of var. modestus lies entirely within that of var. amphioxys and seems that much more open to criticism. It may possibly consist of no more than an arbitrary selection of small-flowered populations. It should be noted, however, that var. amphioxys seems that much more open to criticism. It may possibly consist of no more than an arbitrary selection of small-flowered populations. It should be noted, however, that var. amphioxys reaches its greatest known flower-size in southern Nevada, and it is necessary to turn to Arizona south of the Colorado or to New Mexico to find specimens approaching var. modestus in length of petals and calyx. There is some evidence that var. modestus occurs at somewhat greater elevations than var. amphioxys in their common area.
Distribution:Nevada United States of America North America| Arizona United States of America North America|