Monographs Details: Astragalus bryantii 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
Discussion:

314.  Astragalus Bryantii

Slender, rather tall, perennial, perhaps of short duration, with a taproot and incipient caudex, strigulose with appressed or subappressed hairs up to 0.5-0.9 mm. long, the stems and herbage green or cinereous, the leaflets ± bicolored, usually of a yellowish-green hue and glabrous above, darker green and thinly to densely pubescent beneath; stems several, erect or ascending, (3) 3.5-8 dm. long, simple or nearly so above the base, floriferous upward from near or above the middle; stipules 3-8 mm. long, the lowest early becoming papery and brownish, decurrent around half to the whole stem’s circumference but free, the median and upper ones herbaceous, thinly membranous-margined, with lance-, ovate-, or deltoid-acuminate, mostly recurved or reflexed blades; leaves (4) 6-12 cm. long, petioled or the upper ones often subsessile, with (7) 11-21 ovate, obovate, suborbicular, or broadly elliptic, truncate-emarginate or shallowly retuse, flat leaflets (3) 5-15 mm. long; peduncles ascending, 4-8.5 (10) cm. long, shorter than the leaf; racemes loosely and openly 12-22-flowered, the flowers early spreading or a trifle declined, the axis early elongating, (4) 6-13 cm. long in fruit; bracts lanceolate-, ovate-, or linear-acuminate, membranous-margined, 2-3.5 mm. long; pedicels at anthesis ascending, 0.5-1.1 mm. long, in fruit ascending or a little arched outward, thickened, 1-3-mm. long, persistent; bracteoles 0-2, minute when present; calyx 7-9.3 mm. long, strigulose with black or mixed black and white hairs, the slightly oblique disc 1-1.5 mm. deep, the deeply campanulate or subcylindric tube 5.1-6.4 mm. long, 2.6-3.3 mm. in diameter, the slenderly subulate teeth (1.6) 1.9-3.4 mm. long, the whole becoming papery, ruptured, marcescent; petals purple, drying violet (sometimes pale), the wing-tips paler than the banner or white; banner recurved through ± 40-45°, rhombic-obovate or -oblanceolate, notched, (13) 14—19.5 mm. long, 7.4-10 mm. wide; wings (shorter or exceptionally a trifle longer than the banner) 12.6-16.5 mm. long, the claws 5.6-7 mm., the linear, linear-oblanceolate or -elliptic, obtuse, nearly straight blades 8.7-11 mm. long, 1.8-3 mm. wide; keel 11.6-15 mm. long, the claws 5.6-7.1 mm., the lunately half-obovate blades 6.6-8.5 mm. long, 2.6-3.9 mm. wide, incurved through 75-85° to the broadly rounded apex; anthers 0.6-0.8 mm. long; pod horizontally spreading or widely ascending, sessile on the slightly elevated receptacle or incipient gynophore (up to 0.7 mm. long), linear or linear-lanceolate in profile, almost straight to gently incurved, (1.5) 2-2.7 (3) cm. long, (2.5) 3-5 mm. in diameter, broadly cuneate or rounded at base, abruptly acute or acuminate distally, compressed-triquetrous with nearly flat lateral faces and narrower, deeply grooved dorsal one, carinate ventrally by the suture, the lateral angles narrow but obtuse, the thin, green or often purple-speckled valves becoming papery, stramineous, delicately cross-reticulate, thinly strigulose to glabrous, inflexed as a complete septum 1.5—3.2 mm. long, the beak unilocular; ovules 22—27; seeds orange-brown, sparsely pitted, dull, 2-2.5 mm. long. Collections: 5 (o); representative: Eastwood 5991 (CAS, F, GH); Xerpha M. Gaines 828, 1005, 1009 (Ariz. State College Herb.)

In sand, on talus, or on steep rock-strewn slopes, ± 2500—5000 (perhaps 6000) feet, local, known only from the canyons of the Colorado River in southeastern Utah (Lost Eden Canyon and West Creek in Glen Canyon) and northern Arizona (Phantom Canyon and Clear and Hermit Creeks in Grand Canyon).— Map No. 141.—December to early June.

Astragalus Bryantii (Harold Child Bryant, 1886- ) Barneby in Proc. Calif. Acad. Sci. IV, 25: 156, Pl. 17, figs. 10-18. 1944.—"Arizona: at the head of Phantom Canyon in the Grand Canyon of the Colorado River, Coconino Co., 15 Dec. 1939. Collected by Dr. H. C. Bryant ... "—Holotypus, CAS! isotypus, US!

The Bryant milk-vetch is the only large-flowered perennial member of its section known to occur in the canyons of the Colorado. It is likely to be confused there only with A. lentiginosus var. palans, the pod of which is terete or only a trifle compressed laterally, with convex rather than almost flat lateral faces, and a rounded or subdidymous rather than compressed-triangular section. The species is easily distinguished from the related but allopatric A. nothoxys by its taller, ascending or erect stems and much larger flowers, which resemble those of the Mexican A. Pringlei in length but are much more numerous and more loosely racemose. The pod of A. Bryantii varies a good deal in width and in outline from truly linear to lanceolate. It may be straight or nearly so, but is commonly incurved into a shallow crescent. The valves are ordinarily pubescent, at least thinly so; however, part of the type-collection has pods truly glabrous from the first.