Astragalus albulus Wooton & Standl.
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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
"Type in the U. S. National Herbarium, No. 690252, collected in a canyon on the road to Zuni some distance south of Gallup, August 1, 1904, by E. O. Wooton." Holotypus, US!
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Synonyms
Batidophaca albula (Wooton & Standl.) Rydb.
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Description
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Species Description - Tall and robust, with a thick, woody taproot and shortly forking, at length suffruticulose caudex, densely strigulose and strigose-pilose throughout with short, straight, appressed, together with longer, straight or sinuous, subappressed or ascending hairs up to 1-1.5 (1.7) mm. long, the stems and herbage cinereous or canescent, the leaflets pallid green and glabrous above; stems several or numerous, erect and strictly ascending in well-furnished clumps of bushy outline, (1.5) 2.5-7 dm. long, branched or spurred at nearly every node preceding the first peduncle, the more vigorous branches again branched or spurred; stipules scarious, pallid, fragile in age, 2.5-10 mm. long, all amplexicaul and connate through ± 3/4 their length into a shortly bidentate (sometimes tardily ruptured) sheath; leaves 3—10 (14) cm. long, all but the lowest subsessile, with (7) 11-23 linear, linear-oblanceolate, or narrowly elliptic, acute or subobtuse, mostly folded leaflets (2) 4—27 (in cultivation up to 45) mm. long; peduncles erect, 1.5-4 (5.5) cm. long, much shorter than the leaf; racemes at first densely, at full maturity rather loosely (9) 15—47 flowered, the flowers at full anthesis ascending, the axis elongating, (2) 3-15 (20) cm. long in fruit; bracts scarious, broadly ovate or broadly lance-acuminate, boat-shaped, (2) 3—7 mm. long; pedicels at anthesis ascending, 0.3—0.6 mm. long, in fruit arched outward, a little thickened, 0.6-1.2 mm. long; bracteoles 0-2, sometimes large and conspicuous; calyx (7.2) 7.5—11 mm. long, strigulose or pilosulous (pilose) with white and rarely a few black hairs, the oblique disc (1) 1.2—2 mm. deep, the tube (5.4) 5.7—7.4 mm. long, 3.2—4.2 mm. in diameter, dorsally distended at base but scarcely gibbous, the narrowly subulate teeth (1.5) 1.8—3.6 mm. long, the whole becoming papery-scarious, ruptured, marcescent, petals whitish, the keel-tip faintly maculate; banner rhombic-oblanceolate, shallowly notched, 13-17.2 mm. long, (6.2) 6.6-9 mm. wide; wings 12.5-15.3 mm. long, the claws (5.3) 5.8-7.3 mm., the linear-oblong or -lanceolate, obtuse, nearly straight blades 7.8-9.5 mm. long, 2-2.5 mm. wide; keel 10.4-12.8 mm. long, the claws 5.6—7.4 mm., the half-obovate blades 5.5—6.4 mm. long, (2) 2.3—2.7 mm. wide, abruptly incurved through 90—95° to the bluntly deltoid apex; anthers (0.55) 0.6-0.8 mm. long; pod declined or pendulous, stipitate, the stipe 0.7-2.5 mm. long, the body narrowly ellipsoid or lance-ellipsoid, gently incurved, 9-12 mm. long, 3.3—5 mm. in diameter, cuneate at base, acuminate distally into a triangular, laterally compressed, cuspidate beak, otherwise obcompressed and subtrigonous, carinate ventrally by the slender but prominent suture, openly but often deeply sulcate dorsally, the thin, green, sparsely to densely strigulose, more rarely glabrous valves becoming papery, brownish-stramineous, finely cross-reticulate, not inflexed; seeds brown, smooth or sparsely pitted, not highly lustrous, 2.6—3.3 mm. long.
Distribution and Ecology - Gullied badlands and sandy clay talus under cliffs, in selenium-bearing soils derived from shale or sandstone, 5300-7500 feet, forming colonies in scattered stations on both slopes of the Continental Divide in northwestern New Mexico and northeastern Arizona, from the Rio Grande Valley near Sante Fe north into Rio Arriba County, west to the headwaters of the Little Colorado River and to Black Mesa in Apache and Navajo Counties.—Map No. 44.—July to October.
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Discussion
The Cibola milk-vetch, A. albulus, is easily known by its combination of tall branching stems, dolabriform vesture, connate stipules, and shortly peduncled racemes of many whitish flowers subtended by prominent scarious, boat-shaped bracts. It is furthermore the only tall astragalus of its region likely to be found in flower and fruit from midsummer onward in the badlands. In places it is locally plentiful, commonly associated with Eriogonum leptophyllum Nutt. or some other suffruticose buckwheat of the E. effusum group and flowering with them. In spring the plants appear as neat but vigorous clumps of leafy stems, obviously healthy and obviously of the genus, but puzzlingly sterile to the unaware observer. At full anthesis they become a handsome sight, because of the number of racemes produced in succession from July or August onward until frost.
The earliest collection of A. albulus was made in 1882 at Fort Wingate, New Mexico, by Dr. Washington Matthews, surgeon at the post. The specimen (Matthews 12, GH) was in flower and left unidentified by Watson. Jones mentioned it (1923, p. 257) as representing a probably distinct relative of A. coahuilae, to which it bears no relationship; it was subsequently referred by Rydberg (1927, p. 22) to A. arizonicus, a species endemic to the Gila Basin.
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Objects
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Distribution
Arizona United States of America North America| New Mexico United States of America North America|