Astragalus missouriensis

Title

Astragalus missouriensis

Authors

Rupert C. Barneby

Scientific Name

Astragalus missouriensis Nutt.

Description

225.  Astragalus missouriensis

Low, loosely tufted or prostrate, shortly caulescent or sometimes subacaulescent, with a taproot and at length loosely forking, scarcely suffruticulose caudex (the branches occasionally up to 2 dm. long, usually much shorter), densely strigulose or strigose throughout with straight, parallel, often contiguous, lustrous hairs up to 0.7-1.25 mm. long, the herbage silvery-white to greenish-gray, the leaflets subequally pubescent on both sides; stems of the year commonly somewhat developed (in some young or starveling individuals reduced to sessile crowns), up to 1.5 dm. long, mostly shorter, prostrate and radiating, the internodes sometimes concealed by stipules, but some, especially those preceding the peduncles, up to 1.5-2.5 cm. long; stipules (2) 3-9 mm. long, firm or submembranous, becoming scarious or papery and brownish, ovate or triangular-acuminate, fully or semi-amplexicaul-decurrent, free (or the lowest exceptionally shortly connate); leaves (2) 4-14 cm. long, with flaccid, deciduous or weakly persistent petiole and (5) 11-17 (21) elliptic to narrowly obovate, acute or mucronulate, sometimes mostly obovate and obtuse, flat leaflets 3.5-13 (17) mm. long; peduncles (1.5) 3.5-11 cm. long, usually stout, stiff, and persisting into a second season, ascending in flower, prostrate in fruit; racemes loosely but shortly, sometimes subumbellately (3) 5-15-flowered, the flowers ascending or in age spreading, the axis little elongating, (0.5) 1-4 cm. long in fruit; bracts membranous with green midrib, narrowly lance- or rarely ovate-acuminate, 2.5-8 mm. long; pedicels mostly straight and ascending, rarely a little arched outward, 1-1.7 mm. long at anthesis, thickened, persistent, 1.8-3.5 mm. long in fruit; bracteoles 0-2, sometimes conspicuous; calyx 5-12 mm. long, strigulose with mixed black and white, or more rarely all white hairs, the somewhat oblique disc 1-1.6 (2) mm. deep, the purple-tinged tube cylindric or deeply campanulate, the subulate or less commonly deltoid teeth 0.7-3.3 (5.3) mm. long; petals (except in rare albinos) pink-purple, with a pale lozenge in the fold of the banner, drying dull bluish; banner recurved through ±45°, rhombic-ovate, obovate-cuneate, or broadly elliptic-oblanceolate, 9.5-22 (24) mm. long; wings nearly as long to considerably shorter, the blades narrowly oblong or lance-oblong, obtuse, slightly incurved in the distal half; keel 8.9-17.3 (18.5) mm. long, the lunately half-obovate blades 5.3-8 (9) mm. long, incurved through ± 90-95° to the rounded apex; anthers (0.5) 0.55-0.8 mm. long; pod ascending (humistrate), sometimes through accidental twisting of the pedicel apparently spreading or declined, sessile and (commonly) persistent on the receptacle, subsymmetrically or (in one var.) obliquely oblong or oblong-elliptic in outline, 1.4-2.7 (3) cm. long, (4) 5-9 (10) mm. in diameter, obtuse or sometimes cuneate at base, abruptly contracted distally into a subulate, pungent, or triangular-acuminate and laterally compressed beak, variably compressed, the green, fleshy, strigulose valves becoming stiffly leathery or subligneous, 0.3—0.5 mm. thick when dry, transversely reticulate and wrinkled lengthwise, brownish and ultimately black, either not inflexed, or often so far so as to form a distinct septum up to 1.1 mm. wide; dehiscence primarily through the beak, ultimately downward through the distal half or whole length of the ventral suture, the tips of the valves twisted outward in age, the dorsal suture also inclined to split and expose the endocarp or the outer (conduplicate) walls of the septum; ovules (33) 36-50 (56); seeds brown, pitted or wrinkled, somewhat lustrous, 2-3 mm. long.

Over the greater part of its immense range east of the Continental Divide, the Missouri milk-vetch is a comparatively stable species. In the middle Rio Grande Valley in New Mexico and thence northwestward into Colorado, the racial situation is suddenly complicated by striking mutations and possibly by hybridization with A. amphioxys. Three varieties have been recognized.