Astragalus quinqueflorus

  • Title

    Astragalus quinqueflorus

  • Author(s)

    Rupert C. Barneby

  • Scientific Name

    Astragalus quinqueflorus S.Watson

  • Description

    141. Astragalus quinqueflorus

    Perennial but of short duration, often (perhaps always) flowering the first season, similar to A. Brandegei in habit, cinereously or canescently strigulose with rather coarse, straight, silvery hairs up to 0.3-0.5 (0.6) mm. long, the leaflets sometimes glabrous above; stems eventually numerous, usually freely branched at base, radiating from the root-crown or shortly forking caudex, (1) 2—10 (15) cm. long, the lower intemodes very short, the upper ones reaching (but seldom) 2 cm. in length; stipules subherbaceous becoming papery, deltoid, ovate, or lanceolate, 1.5—3 mm. long, semi- or the lowest ones fully amplexicaul, free; leaves (2) 3-17 cm. long, with very slender petiole and rachis, and 5-11 distant, linear or linear-oblong, obtuse or retuse, folded or involute leaflets 2-20 (25) mm. long, the terminal one commonly longest; peduncles filiform, the lowest (often arising from short lateral spurs) 1—2.5 cm. long, the later ones elongate, up to 10 (17) cm. long, usually surpassing the foliage; racemes loosely 1-7-flowered, the axis little elongating, up to 3 (4) cm. long, in fruit; bracts ovate, 0.5-1.3 mm. long; pedicels very slender, ascending, straight or flexuous, at anthesis 0.6-1.5 mm., in fruit 1.6-2.4 long; calyx 2.6-3.6 mm. long, white-strigulose, the subsymmetrically obconic disc 0.5—0.7 mm. deep, the tube 1.5—2 mm. long, 1.3—1.6 mm. in diameter, the subulate teeth 0.8-1.6 mm. long, the whole becoming papery, ruptured, marcescent; petals whitish with lilac wing- and keel-tips; banner recurved through ± 50°, oblanceolate or rhombic-ovate, shallowly notched, 4.5-5.4 mm. long, 2.8-3.8 mm. wide; wings 4.2—4.6 mm. long, the claws 1.5-1.8 mm., the narrowly oblong, obtuse blades ± 3-3.2 mm. long, 1-1.3 mm. wide, both incurved but the left one more abruptly and further than the right; keel 3.2-3.8 mm. long, the claws 1.3-1.8 mm., the half-circular blades 1.7-2 mm. long, 1.6-2.2 mm. wide, incurved through 110-120° to the deltoid, obscurely porrect apex; anthers 0.2-0.35 mm. long; pod pendulous (or when humistrate irregularly ascending), sessile, obliquely ovoid or oblong-ellipsoid, straight or a trifle decurved, 6-10 (11) mm. long, 3-4.5 mm. in diameter, rounded at base, contracted distally into a very short, declined, subulate, cusplike beak, laterally compressed-triquetrous, keeled ventrally by the prominent, strongly convex suture, shallowly sulcate dorsally, the lateral faces low-convex, the lateral angles obtuse, the thin, green, white-strigulose valves becoming papery, stramineous, faintly reticulate, inflexed as a very narrow partial septum 0.2-0.5 mm. wide; seeds brown or olivaceous, sometimes purple- speckled, wrinkled and angulate, sublustrous, 1.6-2.4 mm. long.— Collections: 10 (iv); representative: Pringle 711 (G, K, ND, NY, P, US); Palmer 25 (NY, US, p. p.); Johnston 8821 (GH); Purpus 136 (MO, POM, US); Ripley & Barneby 13,475 (NY, RSA), 13,507 (CAS, MICH, NY, RSA, US).

    Plains and valley floors, 2500-8400 feet, commonly in grama-grassland, on granitic or rarely calcareous bedrock, locally plentiful but inconspicuous and probably often overlooked, southcentral Chihuahua and western Coahuila south to Durango and Zacatecas.—Map. No. 56.—April to November, flowering either after spring or summer rains.

    Astragalus quinqueflorus (five-flowered) Wats. in Proc. Amer. Acad. 21: 450. 1886. —"On the hills and plains near Chihuahua, Pringle, April 1885 (No. 234)."—Holotypus, GH! isotypi, NY, US!—Phaca quinquefiora (Wats.) Rydb. in N. Amer. Fl. 24: 361. 1929.

    The five-flowered milk-vetch, A. quinqueflorus, bears a close resemblance only to the kindred A. Brandegei with which it shares a delicate, loosely tufted growth-habit, few, distant leaflets, and few, tiny, remotely racemose flowers tipped and faintly suffused with lilac. It differs from its relative in the shorter, subunilocular pod, which is normally more strongly compressed laterally and hence yields an obtusely triangular rather than obcompressed-reniform section. As in A. Brandegei, the plants flower precociously and apparently are often monocarpic although capable, when conditions are favorable, of enduring into a second year. The septum within the fruit of A. quinqueflorus is inconspicuous but always present and no narrower than that long recognized and described in many Strigulosi and Oroboidei.