Monographs Details: Astragalus iodanthus var. vipereus 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:Latin Diagnosis - a var. iodantho floribus minoribus et legumine angustiori, ut supra descriptis, absimilis.

Variety Description - Variable in pubescence, but the stems nearly always finely cinereous; leaflets (7) 9-13 (15), mostly broad and retuse; calyx (3.3) 3.7-5.3 mm. long, the disc 0.6-0.9 mm. deep, the shortly campanulate tube 2.6-3.2 mm. long, 1.7-2.6 (2.9) mm. in diameter, the teeth (0.6) 1-2.2 mm. long; petals pale lilac, the keel-tip commonly more deeply colored than the rest; banner 9—11.5 mm. long, 5.3—8.3 mm. wide; wings as long or not over 1 mm. shorter, the claws 2.4-3.7 mm., the blades 6-7.3 mm. long, 1.8-2.4 mm. wide; keel 7.8-10 mm. long, not over 1.5 mm. shorter than the banner, the claws 2.9—4.1 mm., the blades 5.4—7.1 mm. long, 2.3-3.1 mm. wide; pod (2) 2.5-3.5 (4) cm. long, (2.5) 3-5.5 (6) mm. in diameter, the compression mostly triquetrous; ovules 14-24.

Distribution and Ecology - Barren stony hills, knolls, and gullied river bluffs, in stiff alkaline clay soils, 2600-4200 feet, locally common along the Snake, Bruneau, Malheur, and Owyhee Rivers, in Twin Falls, Elmore, and Owyhee Counties, Idaho, and adjoining Malheur County, Oregon.--Map No. 133.--April to June.

Discussion:Even though no better quantitative character than the length of the calyx-tube is absolutely diagnostic of var. vipereus, it is unquestionably a distinct entity, with its own indefinable facies and a range disjunct from that of var. iodanthus. The first collections that came to my notice were identified as the now discarded var. diaphanoides, which they resembled in their weakly graduated or subequal petals, but the petals themselves are with few and irrelevant exceptions smaller and shorter, the leaflets usually less numerous, the stems more densely strigulose, and the pod nearly always narrower and more sharply trigonous. The differences between var. iodanthus and var. vipereus become impressive only when plants of comparable age and vigor are compared. It is a simple matter to pick out a few small and narrow pods, for example, from a starveling plant or a late raceme of var. iodanthus which fall below the average within the colony, and similarly an occasional fruit of var. vipereus which exceeds in width the norm for its kind. Such exceptions, narrowly interpreted, may appear at times to invalidate the differential criteria stressed in the key. As in the typical variety, the vesture of var. vipereus is variable in quality. Normally composed of straight, appressed hairs, it is occasionally curly and villosulous. The latter state is apparently rare, known at present only from the bluffs of the Owyhee River near Rome, Malheur County, where it is a constant feature of the local populations.
Distribution:Idaho United States of America North America| Oregon United States of America North America|