Monographs Details: Astragalus beckwithii var. sulcatus 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 - legumine in gynophoram graciliorem abrupte contracto nec per collum obconicum sensim attenuato, dorso angustius profundiusque sulcato insignis, caeterius var. weiserensi Jones praesimilis.

Variety Description - Similar to var. weiserensis; stems (2) 3—4 dm. long; stipules 3-8 mm. long; leaflets broadly rhombic- or oblong-ovate, obtuse or mucronulate, 0.7-2.4 cm. long; bracts 2-4 mm., bracteoles up to 2 mm. long, sometimes 0; calyx nearly glabrous except for a few black hairs on and within the teeth, 10.8-12.8 mm. long, the tube 6.2-6.8 mm. long, ± 5 mm. in diameter, the teeth 4-6.6 mm. long; petals cream-colored, the banner 18—20 mm., the wings 18.6-19 mm., the keel 14.5-14.8 mm. long; pod elevated on a slender gynophore 4—5 mm. long, the body lunately oblong, incurved through ¼-½-circle, 2-2.5 cm. long, 6-7.5 mm. in diameter, the dorsal face sulcate from base to beak, the valves mottled.

Distribution and Ecology - Open brushy slopes, on volcanic gravelly clay soils, 3600-4500 feet, locally plentiful but known only from the banks of the Salmon River in eastern Lemhi County, Idaho, from North Fork upstream about 40 miles.—Map No. 106.—May to July.

Discussion:

The valley of the upper Salmon River, as it flows northward through Custer and Lemhi Counties from Clayton to the westerly bend at North Fork, is of particular interest to the botanical geographer on account of locally endemic plant species (including in our genus A. amblytropis and A. aquilonius), not to mention the presence of several forms of which the main range lies well to the south in the Great Basin. These southern elements may have reached the valley during a recent xerothermic period when a more southern flora was able to spread northward across the low Salmon-Lost River watershed. Subsequent isolation, which followed a change in climate, may have enabled some of these, in the presence of a richly varied choice of soils and rock formations and newly emerging habitats created by rapid erosion of the valley floor, to evolve in new directions. The disjunct occurrence of var. weiserensis in British Columbia, which follows an established pattern of plant distribution in the region, shows that A. Beckwithii was more widely dispersed northward than at the present time, and it is reasonable to suppose that var. sulcatus represents the modified progeny of a relict population dating from the same diaspora.

It has been pointed out above that var. Beckwithii and A. oophorus var. caulescens are virtually indistinguishable until the fruit has formed; the same can be said of A. Beckwithii var. weiserensis and var. sulcatus. These are only two instances of mutations that find external expression in the pod alone. It is small wonder that a system of classification based on the astragalus pod, without reference to other features of the plant-body, can only be partly realistic and is, in practice, often unnatural.

Distribution:Idaho United States of America North America|