Astragalus humistratus var. humivagans

  • Title

    Astragalus humistratus var. humivagans

  • Authors

    Rupert C. Barneby

  • Scientific Name

    Astragalus humistratus var. humivagans (Rydb.) Barneby

  • Description

    100c. Astragalus humistratus var. humivagans

    Densely strigulose and appressed-pilose or -pilosulous throughout, the hairs straight or nearly so and up to 0.8—1.4 (1.7) mm. long (the longest sometimes narrowly ascending or exceptionally spreading, the shortest rarely sinuous- crispate), the herbage cinereous, canescent, or silvery-silky; stems (0.6) 1-6 (8) dm. long; stipules (1.5) 2-9 mm. long; leaves (1) 1.5-6 (7.5) cm. long, the (7) 17 (19) leaflets (2) 5-17 (19) mm. long; peduncles 2—9 cm. long; racemes (3) 7-22-flowered, the axis 1-9 (13) cm. long in fruit; calyx (4.5) 5-7.4 (8.8) mm. long, the disc 0.6-1.2 mm. deep, the tube (2.4) 2.7-3.7 (4.1) mm. long, 2.1-3.2 (3.5) mm. in diameter, the teeth (1.4) 1.9-3.6 (5) mm. long; petals greenish-white or ochroleucous, commonly lined, suffused, or distally margined with dull purple, rarely all bright purple; banner 7.2-10.2 (11.6) mm. long, (5) 5.5-8.4 (9) mm. wide; wings (6.8) 7.4-9.5 (10) mm. long, the claws (2.2) 2.4-3.6 mm., the blades (4.4) 5-6.5 (7.1) mm. long, (1.5) 1.8-2.8 mm. wide; keel (6) 6.4-8.5 (9.1) mm. long, the claws 2.4-3.5 (3.8) mm., the blades (3.8) 4-5.6 (6) mm. long, 2.2-2.7 (3) mm. wide, the apex narrowly triangular or lanceolate and beaklike; anthers (0.4) 0.45-0.65 (0.7) mm. long; pod obliquely ovoid, obovoid, half-ovoid, or oblong-ellipsoid, (6) 8-14 mm. long, (3) 3.5-5.7 mm. in diameter, somewhat obcompressed in the lower half or third, either lunately incurved or straight below the deltoid or lance-acuminate, incurved beak, dorsally flattened or sulcate at base or from base to middle, the ventral suture acute and prominent, the valves thinly to quite densely strigulose with straight and appressed, or with incumbent and somewhat twisted hairs; ovules 10-16.—Collections: 32 (xi); representative: Clokey 8408 (NY, RSA); Jones 5204 (NY, POM); Eastwood & Howell 7205 (CAS); Ripley & Barneby 8462 (CAS, RSA); M. & G. Ownbey 3005 (RSA, WS); Ripley & Barneby 12,635 (CAS, RSA), 12,911 (CAS, NY. RSA)

    Dry gravelly or sandy slopes and flats, chiefly with juniper and piñon but ascending southward into yellow pine forest, strongly calciphile north and west of the Colorado River but elsewhere occurring mostly on basalt or other rock, (4450) 4900-8000 feet, widespread and locally plentiful in northwestern Arizona and southwestern Utah, extending less commonly northwest into eastcentral and southern Nevada and southeast to the Little Colorado-Gila-Rio Grande watershed in eastcentral Arizona and adjoining New Mexico.—Map No. 41B.—May to September, but much more abundant in spring than after summer rains.

    Astragalus humistratus var. humivagans (Rydb.) Barneby in Amer. Midl. Nat. 55: 478. 1956, based on Batidophaca humivagans (spreading on the ground) Rydb. in N. Amer. Fl. 24: 316. 1929.—"Type collected at Mokiak Pass, Arizona, in 1877, Palmer 108..."— Holotypus, GH! isotypi, NY, US!—A. humistratus var., Gray in Proc. Amer. Acad. 13: 369. 1878.

    Westward and northward from the Grand Canyon, var. humivagans is the only representative of the ground-cover milk-vetch and is found almost exclusively on limestone in the pinon belt. In central Arizona it is sympatric with var. Hosackiae, which has similar pods but green foliage. Southeastward along the Mogollon Escarpment, in soils mostly of volcanic origin, it overlaps the range of vars. humistratus and crispulus, although it is ordinarily found at lower elevations than either of the latter. At anthesis it resembles var. sonorae very closely, but a count of the few ovules will presage a characteristically short pod; the two silvery varieties, however, are not known to occur in the same area. The var. humivagans varies greatly in stature. A form with exceptionally large flowers occurs on Kanab Plateau and near Mount Trumbull in Mohave County, Arizona (Peebles & Parker 14,730; McClintock 52-486, both CAS), and a gigas phase, in which large flowers are combined with greatly elongated calyx- teeth, was found growing with typical plants in the White Mountains (Barneby 5047 (gigas), 5048 (normal), both RSA). The pod varies from green to purplish or reddish when fresh, or is sometimes brightly mottled.