Astragalus scopulorum

  • Title

    Astragalus scopulorum

  • Authors

    Rupert C. Barneby

  • Scientific Name

    Astragalus scopulorum Porter

  • Description

    37. Astragalus scopulorum

    Of moderate stature, thinly strigulose with straight, filiform, appressed and subappressed hairs up to 0.5-0.75 mm. long, the stems usually purplish-brown, the herbage green, the leaflets somewhat bicolored, brighter green and glabrous above; stems several, decumbent and radiating, 1.5-4.5 dm. long, slender, simple, and subterranean for a space of 3-13 cm., thereafter becoming stouter and divaricately branched or upwardly bearing short, sterile, or depauperately fertile spurs in most of the axils, flexuous but not abruptly zigzag distally; stipules 3-9 mm. long, the subterranean ones pallid and scarious, the upper ones rather firm, the lowest of the stems and branches connate-amplexicaul into a stiffly papery, several-nerved, subtruncate or bidentate sheath, this sometimes ruptured by expansion of the stem, the median and upper ones mostly smaller, narrower, less strongly connate, the uppermost often free, with deltoid or lance-acuminate, acute or obtuse, erect or squarrose blades; leaves (1.5) 2.5-8 cm. long, the lowest shortly petioled, the rest subsessile, with (7) 15-29 (35) oval-oblong to linear-elliptic or oblanceolate, subacute, sharply acute, or rarely obtuse, flat or loosely folded leaflets (2) 4-18 mm. long; peduncles erect or incurved-ascending, 2.5-14 cm. long, a little shorter to much longer than the leaf; racemes (5) 10-22-flowered, rather dense at early anthesis, the declined or nodding flowers secund and retrorsely imbricated, the axis somewhat elongating, (1) 2-7 cm. long in fruit; bracts membranous or membranous-margined, lanceolate or lance-caudate, (1.5) 2—7 mm. long; pedicels at anthesis ascending and 1.5-2.5 (3) mm. long, in fruit arcuately spreading or straight and divergent, a little thickened, 2-4 mm. long; bracteoles 0-2; calyx (8) 9-11.5 (14) mm. long, strigulose with black or sometimes with some or all white hairs, the oblique disc 0.9-1.6 mm. deep, the deeply campanulate or subcylindric, pallid tube (6.5) 6.8-8.5 mm. long, 3.2-4.1 mm. in diameter, basally truncate and attached at the dorsal corner, sometimes a trifle saccate behind the pedicel, the subulate or lance-acuminate teeth 1.5-3.5 (6) mm. long; petals ochroleucous, the keel-tip sometimes faintly maculate; banner recurved through ±45°, lance-oblong or rhombic-oblanceolate, 18.3-23.5 mm. long, 6-8.5 mm. wide; wings 16.4-19 mm. long, the claws 8.5-10.5 mm., the oblong-oblanceolate, obtuse, nearly straight or gently incurved blades 8.3-9.6 mm. long, 2.3-3.2 mm. wide; keel 13.6-15.4 mm. long, the claws 7.7-9.5 mm., the half-obovate or obliquely obovate blades 5.5-6.6 mm. long, 2.9-3.3 mm. wide, incurved through 80-95° to the deltoid apex; anthers 0.7-0.9 mm. long; pod pendulous, stipitate, the straight, slender stipe (4) 5-9 mm. long, the body linear-oblong, -elliptic, or -oblanceolate in profile, nearly straight or lunately incurved, (1.8) 2.5-3.5 cm. long, 3-6.5 mm. in diameter, cuneate at both ends or (when narrow) acuminately tapering downward into the stipe, cuspidate at apex, triquetrously compressed, with acute ventral and narrow but obtuse lateral angles, the lateral faces flat or low-convex, the slightly narrower dorsal face sulcate or shallowly concave, the thin, green, sometimes purple-speckled, glabrous valves becoming papery, greenish-stramineous or ultimately brown, transversely reticulate, inflexed as a complete septum 2-4 mm. wide; seeds brown, sometimes obscurely purple-dotted, smooth, lustrous, about 3-3.5 mm. long.—Collections: 41 (xi); representative: Rydberg & Garrett 9152 (NY); Rydberg & Vreeland 5981 (NY, WS); Baker, Earle & Tracy 69 (ND, NY); W. A. Weber 4752 (CAS, SMU, TEX, WS); Ripley & Barneby 5329, 8329, 10,510 (CAS, RSA); Barneby 12,618 (CAS, NY, RSA).

    Gravelly clay flats and hillsides, in oak thickets, among sagebrush, in piñon or more rarely open pine forest, in soils of granitic or occasionally of basaltic or sedimentary origin, rather common and locally abundant at 6800-10,550 feet in the valleys of the Rocky Mountains from the upper Grand River and headwaters of the South Platte in Colorado, south on both slopes of the Divide (but more common westward), to the Sandia and Manzano Mountains in northcentral New Mexico, west to the La Sal and Abajo Mountains in eastern Utah and the Black Mesa in northern Apache County, Arizona; apparently disjunctly, at 4800-5400 feet, along the upper forks of the Salt River in southern Apache and adjoining Gila Counties, Arizona; also local on the west slope of the Wasatch in central Utah (Salina Canyon, Sevier County; base of Mt. Nebo, Juab County; Thistle, Utah County).—Map No. 13.—May to August.

    Astragalus scopulorum (of craggy rocks, symbolizing the Rocky Mountains) Port. in Port. & Coult., Syn. Fl. Colo. 24. 1874.—"South Park, July 24, 1872, Porter. Wet Mountain Valley, 1873, Brandegee, in flower and fruit."—Cotypi, PH! isotypi (Porter, Brandegee), NY!— Tragacantha scopulorum (Port.) O. Kze., Rev. Gen. 948. 1891. Tium scopulorum (Port.) Rydb. in Bull. Torr. Club 32: 659. 1905.

    Astragalus subcompressus (somewhat flattened, of the pod) Gray ap. Brand. in Bull. U. S. Geol. Surv. 23 : 234. 1876.—"Animas Valley, 7000 feet altitude."—Holotypus, collected by T. S. Brandegee, in 1875, GH! isotypi, Brandegee 1287, UC!

    Astragalus rasus (clean-shaven, the plants supposedly glabrous) Sheld. in Minn. Bot. Stud. 1: 158. 1894.—"Collected near Durango, Colo., June, 1891, by Miss Alice Eastwood, also on the Mesa Verde, southeast Colo., June, 1892, by Miss Alice Eastwood; and at Grand Junction, Colo., June, 1893, by De Alton Saunders."—Holotypus, the first cited, so labeled by Sheldon, MINN! paratypus (Saunders), NY!

    Tium stenolobum (with narrow calyx-lobes) Rydb. in N. Amer. Fl. 24: 388. 1929.—"Type collected in the Sandia Mountains, on the eastern slope of Palomas, New Mexico, Charlotte C. Ellis 326 ... "—Holotypus, US! isotypi (2 sheets), NY!

    The Rocky Mountain milk-vetch, A. scopulorum, is a handsome floriferous species, easily distinguished from others in the same range by the combination of stems arising from a buried root-crown and therefore naked except for stipular sheaths for a space of several centimeters below the first leaf, lower stipules united into a sheath, large, nodding, ochroleucous flowers, and pendulous, stipitate, trigonously compressed pods. The calyx-teeth vary in length from 1.5 to 6 mm., and the leaflets from obtuse to sharply acute, but the form with particularly long teeth and subacute leaflets described as Tium stenolobum is merely one of several minor variants of no taxonomic status. Among the isotypi of T. stenolobum at NY and US are plants with teeth only ± 3 mm. long, average for the species as a whole. Gray’s A. subcompressus, described a second time in 1877 (in Proc. Amer. Acad. 12: 56), was no doubt proposed in ignorance of Porter’s slightly earlier A. scopulorum. No such excuse can be made for A. rasus, distinguished by Sheldon by "the absence of pubescence," although he described the young leaves and stems as at least sometimes thinly hairy. The typus of A. rasus is a characteristic example of the Rocky Mountain milk-vetch which often appears almost or quite glabrous to the unaided eye.

    The range of A. scopulorum outside the Rocky Mountains proper is scattered and discontinuous, and Jones believed the species to be a recent introduction in Utah. Subsequent collections from Utah and the disjunct but unquestionably natural occurrence of A. scopulorum on the Salt River in Arizona shows that Jones was probably mistaken on this point.

    The Rocky Mountain milk-vetch was collected first by Dr. Parry in Middle Park, Colorado, in 1864 (US).