Astragalus ampullarius

  • Title

    Astragalus ampullarius

  • Authors

    Rupert C. Barneby

  • Scientific Name

    Astragalus ampullarius S.Watson

  • Description

    177. Astragalus ampullarius

    Low, slender, strigulose with flattened, tapering, scalelike hairs up to 0.35 mm. long, the lower emersed intemodes and petioles commonly canescent, the herbage green, the leaflets either thinly pubescent or glabrous beneath, glabrous and brighter green above, ciliate; stems solitary or few together, arising directly from the root-crown, subterranean for a space of 3.5-14 cm., at emergence stouter, bearing 1-2 short branches or spurs at the first, usually approximate, aerial nodes, thereafter simple, erect or ascending, above ground 2.5—7.5 cm. long; stipules membranous, pallid, 2.5—6 mm. long, those at the buried nodes connate into a cylindric sheath, the rest amplexicaul and shortly connate, the first above ground ovate, obtuse, the rest drawn out into deltoid or lanceolate free blades, or some upper ones only semiamplexicaul and free; leaves 3-10 (14) cm. long, the petioles commonly widely divaricate, with (7) 11-15 (19) obovate- or ovate-cuneate, rarely elliptic, obtuse or retuse, flat leaflets 6-15 mm. long; peduncles 1 or 2, the upper one appearing terminal, strictly erect, (1) 2—8 (11.5) cm. long; racemes loosely 6-20-flowered, the axis 1.2-13 cm. long in fruit; bracts membranous, lanceolate, 1.5-3 mm. long; pedicels at anthesis 1—1.7 mm. long, in fruit thickened, straight, ascending, 1.8—3 mm. long; bracteoles 2; calyx 4.8—7 mm. long, thinly black-strigulose, the oblique disc 0.7—1 mm. deep, the membranous tube 4.2—6 mm. long, 2.5-3.5 mm. in diameter, the subulate dorsal tooth 0.5-1 mm. long, the rest either similar, or shorter and deltoid, the orifice oblique, the whole becoming papery, marcescent unruptured; petals all ochroleucous, or purple with white wing- tips and pale, striate eye in the banner, if purple drying violet; banner elliptic or rhombic-elliptic, 13.5-20 mm. long, 5.6-6.8 mm. wide; wings 10.6-18.3 mm. long, the claws 4.4—7.2 mm., the lance-oblong or oblong-oblanceolate blades 7.4-12.5 mm. long, 2.2-2.5 mm. wide; keel 9-12.2 mm. long, the claws 3.3-7 mm., the lunately half-obovate blades gently incurved through 80-90° to the rounded apex; anthers 0.55-0.65 mm. long; pod erect, stipitate, the slender, nearly straight stipe 9-19 mm. long, the body broadly ovoid, oblong-ovoid, or subglobose, strongly inflated, 1.2-2 cm. long, 8-11 mm. in diameter, nearly symmetric but commonly a trifle more convex on the dorsal side, truncate at base, abruptly contracted distally into a short, compressed-conic, cuspidate beak, terete or nearly so, esulcate, the thin, green, purple-dotted, glabrous valves becoming purplish-stramineous, papery, either not inflexed or inflexed near the base as a rudimentary septum up to 0.3 mm. wide, the funicular flange narrow, ± 0.5 mm. wide; seeds light brown, smooth but dull, 2-2.2 mm. long.—Collections: 7 (iii); representative: Eastwood & Howell 9149 (CAS, RSA), 9299 (CAS, RSA, US); Ripley & Barneby 4307, 4802 (CAS, RSA).

    Barren gumbo-clay knolls derived from disintegrated white or red sandstones, associated with Eriogonum subreniforme Wats., Phacelia cephalotes Gray, or both, 3200-5400 feet, rare and local, known only from three (possibly four) narrowly restricted stations along the south base of the Zion Escarpment (Kanab; south of Orderville; east of Washington) in western Kane and Washington Counties, Utah.—Map No. 71.—Late April to June.

    Astragalus ampullarius (flask-shaped, of the pod) Wats. in Amer. Nat. 7: 300. 1873. —"Kanab, Southern Utah, (Mrs. E. P. Thompson)."—Holotypus, GH! isotypus, dated 1872, US!—Tragacantha ampullaria (Wats.) O. Kze., Rev. Gen. 943. 1891. Phaca ampullaria (Wats.) Rydb. in Bull. Torr. Club 40: 47. 1913.

    The singular gumbo milk-vetch, A. ampullarius, occurs in small quantity in a specialized environment and is one of the truly rare astragali. Nearly seventy years elapsed between the original collection at Kanab and rediscovery of the species, in 1941, by Alice Eastwood and John Thomas Howell at the type-locality and in a new station in the Virgin Valley some fifty miles westward. In the following summer Ripley & Barneby established a third locality about twenty-five miles northwest of Kanab. These remain the only stations certainly known. A browsed fragment collected by Ripley on clay mounds near Cedar City in Iron County was thought at the time to be, in all probability, A. ampullarius; but the specimen was lost. The species is to be sought in the foothills of the Kolob Plateau.

    The gumbo knolls, to which A. ampullarius is rigidly confined, are a remarkable geological feature of the sandstone butte country of the Colorado Basin. Often brightly colored in tones of purple, violet, or rosy-lavender, sometimes with alternating belts of arsenical green or sulfurous yellow, they appear from a distance barren of vegetation but play host to some of the most interestingly modified and specialized plants of the region, among them several species of Phacelia and Eriogonum. Howell (in Leafl. West. Bot. 3: 137-8) has described these mounds as representing the comminuted remnants left behind as the vertical front of a sandstone cliff retreats before the stresses of erosion. They are composed of a fine-grained clay, often mixed with rock fragments, but highly retentive of moisture, which turns after spring rains to a stiff putty-like ooze into which the hooves of wandering cattle sink, leaving prints a foot or more deep. As the surface dries out slowly, the crust breaks up into polygonal plates of the form seen on the beds of desiccating pools, but at a depth of a few inches some palpable moisture is imprisoned throughout the summer. The root of the gumbo milk-vetch penetrates deeply into this apparently inhospitable medium. Its crown, bearing the annual points of renewal, is buried at a depth of up to a decimeter, and only a few centimeters of the stems appear above the surface. The leaves, crowded on the stem, are arranged in what I might describe as a loose rosette pressed to the ground; the solitary or sometimes two peduncles rise vertically from near the stem’s apex. The pod of A. ampullarius possesses a delicate beauty because of the length and slenderness of the stipe, which bears aloft the proportionately large and plumply swollen, purple-speckled body.

    In the drainage of Kanab Creek, near Kanab and Orderville, the flowers of A. ampullarius are bicolored, with violet-purple banner and obtuse, white wing-tips, and the calyx-teeth are subulate and of nearly equal length. Near Washington in the Virgin Valley, the petals are ochroleucous, with concolorous, distinctly emarginate wing-tips, and the paired calyx-teeth are shorter and deltoid. The species is confined to so narrow an ecological niche that each population becomes, in effect, an insular endemic as securely quarantined against its nearest neighbor as if separated by leagues of sea. In such circumstances small genetic differences and small mutations may well become established and perpetuated in different colonies.