Astragalus adanus A.Nelson
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Authors
Rupert C. Barneby
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Authority
Barneby, Rupert C. 1964. Atlas of North American Astragalus. Mem. New York Bot. Gard. 13(1): 1-596.
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Family
Fabaceae
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Scientific Name
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Type
".. .in the Boise Hills, No. 260 by Macbride, June 18, 1910."—Holotypus, RM! isotypi, G, GH, MO!
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Synonyms
Ctenophyllum adanum (A.Nelson) Rydb., Cnemidophacos adanus (A.Nelson) Rydb.
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Description
Species Description - Robust and leafy, with a woody taproot and shortly forking, sometimes knotty caudex, thinly pilosulous or loosely strigulose with fine, loosely ascending, incurved, or subappressed hairs up to 0.5-0.7 mm. long, the stems commonly subglabrous, the herbage green or exceptionally gray-silky when young, the leaflets glabrous above, the inflorescence usually fuscous- or black-pubescent; stems several or numerous, erect and ascending in clumps, (2) 2.5-4.5 dm. long, striate, pale green or stramineous in age, composed of 5-10 developed internodes, the whole evidently longer than the inflorescences; stipules membranous, 4-9 mm. long, shortly adnate to the petiole-base, the lowest early becoming papery, decurrent around half to nearly the whole stem’s circumference, the median and upper ones narrower, with triangular or lance-acuminate, erect or deflexed blades, their margins commonly beset with a few minute processes; leaves 7-13 (16) cm. long, the lower ones slender-petioled, the upper subsessile, with (13) 17-27 ovate, oblong, lance-oblong, or broadly elliptic, retuse or obtuse, flat, thin-textured leaflets 6-26 mm. long; peduncles erect, (4) 10-18 cm. long, equaling or commonly surpassing the leaf; racemes (4) 7-22-flowered, the flowers subcontiguous, ascending or subhorizontal at anthesis, the axis early elongating, (2) 3-8 cm. in fruit; bracts membranous, lanceolate or ovate-acuminate, 1.5-3.5 mm. long; pedicels at anthesis slender, 1-1.5 mm. long, in fruit ascending, clavately thickened, 2.5-5 mm. long; bracteoles nearly always 2; calyx 6.9-10.3 mm. long, finely pilosulous with black, fuscous, or partly white hairs, the oblique disc (0.8) 1-1.5 mm. deep, the membranous, subtumid, deeply campanulate to subcylindric tube 5.2-8 mm. long, 3.5-4.4 mm. in diameter, strongly convex dorsally but not gibbous basally, the broadly triangular-subulate to lanceolate teeth 1.6-2.8 mm. long, the ventral pair commonly broadest, the whole becoming papery, fragile, irregularly circumscissile; petals ochroleucous, immaculate; banner recurved through ±45°, broadly rhombic-elliptic or -oblanceolate, 15.5-22 mm. long, 6.2-10.6 mm. wide; wings 13.5-20.2 mm. long, the claws (5.6) 6.5-8.6 mm., the oblong-oblanceolate, obtuse or obliquely emarginate, nearly straight blades 9-13.2 mm. long, 2.7-3.5 mm. wide; keel 11-13.1 mm. long, the claws 5.5-8 mm., the half-obovate blades 5.3-7.7 mm. long, 2.8-3.5 mm. wide, abruptly incurved through 90° to the bluntly deltoid apex; anthers 0.55-0.75 mm. long; pod erect, sessile, obliquely ovoid or oblong-ovoid, 1.3-1.8 cm. long, 5-6 mm. in diameter, obtuse at base, abruptly contracted distally into a short, pungently cuspidate beak, straight or a trifle incurved, a little dorsiventrally (in some dried specimens apparently laterally) compressed, bicarinate by the thick, prominent sutures, esulcate, the green, fleshy, glabrous valves becoming brownish-stramineous, stiffly leathery or subligneous, transversely rugulose-reticulate and often wrinkled lengthwise, not inflexed; ovules 14—18; seeds brown, smooth but punctate, 2.5-3.5 mm. long.
Distribution and Ecology - Brushy slopes, terraces and benches along canyons, or on dry flats and gently rolling hill country among sagebrush, in alluvial clays and gravels of both granitic and basaltic origin, 2700-6000 feet, not rare in southwestern Idaho in the valleys of the Weiser, Payette, and Boise Rivers, east to the head of Camas Creek in Camas County, north just across the crest of the Sawtooth Range in Custer County, and apparently isolated to the south of the Snake River in the Goose Creek Mountains, Cassia County, and at the west base of Mt. Nebo in eastern Juab County, Utah.—Map No. 64.—May to July.
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Discussion
The Boise milk-vetch, A. adanus, is one of several moderately tall, leafy, white-flowered astragali of the intermountain region; lacking any immediately striking feature at anthesis, it is not easily identified without the fruit. The pod is similar in form and in its fleshy, at length subligneous texture to that of A. reventus, but it is shorter and of a more plumply ovate outline. The species varies little, and the populations isolated to the south of the Snake River do not differ perceptibly from those in the main range. The Boise milk-vetch was probably first collected in 1881, in Ada County, by E. V. Wilcox (NY).
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Objects
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Distribution
Idaho United States of America North America| Utah United States of America North America|