Monographs Details: Astragalus ensiformis M.E.Jones
Authors:Rupert C. Barneby
Authority: Barneby, Rupert C. 1964. Atlas of North American Astragalus. Mem. New York Bot. Gard. 13(1): 1-596.
Synonyms:Hamosa ensiformis (M.E.Jones) Rydb.
Description:Species Description - Low but rather coarse, with shallowly buried root-crown or caudex, strigulose with fine, tapering, straight, appressed hairs up to 0.4-0.8 mm. long, the growing tips cinereous, the leaflets bicolored, yellowish-green and glabrescent above, the inflorescence loosely black-pubescent; stems several, simple, 8-13 cm. long, composed of several short, subterranean internodes as long or only 2-3 times longer than the stipules, and 4-5 developed internodes 2-6 cm. long, floriferous from the 2-3 uppermost leaf-axils; stipules dimorphic, the lowest papery, pallid, broadly ovate, obtuse, several-nerved, 4-10 mm. long, amplexicaul-decurrent but free, broader than the stem, the upper ones progressively narrower, subherbaceous, the uppermost lanceolate or narrowly ovate, acute; leaves 5-13 cm. long, petioled but the uppermost shortly so, with 13-17 ovate, obovate, or oblong- obovate, obtuse or retuse, flat, thick-textured leaflets 8-20 mm. long; peduncles at first incurved-ascending, in fruit subhorizontal, 5-12 cm. long; racemes loosely 12-30-flowered, the axis 4-10 cm. long in fruit; bracts submembranous, lanceolate, 2.5-5 mm. long; pedicels at anthesis 1-1.5 mm. long, early arched outward, in fruit 1.5-3 mm. long; bracteoles 0; calyx 7.3-7.7 mm. long, densely black- pilosulous, the disc 0.5-0.6 mm. deep, the membranous, purplish, cylindric tube oblique at base, 6—6.5 mm. long, 2.8—3 mm. in diameter, the subulate teeth 1.2-1.5 mm. long, the ventral pair broadest and shortest; petals sordid purple, the wing- tips paler or whitish; banner recurved through about 45°, rhombic-ovate beyond the cuneate claw, 14—15 mm. long, 7—8.6 mm. wide; wings 12.2—14 mm. long, the claws 6—6.4 mm., the narrowly oblong-oblanceolate, obtuse, nearly straight blades 7.2—8.5 mm. long, 1.8—2 mm. wide; keel 10.5—10.8 mm. long, the claws 5.9-6.2 mm., the half-obovate blades 5.2-5.3 mm. long, 2.5-2.6 mm. wide, incurved through 80—90° to the blunt apex; anthers 0.6—0.65 mm. long; pod essentially pendulous but sometimes ascending when humistrate, shortly and obscurely stipitate, the thick stipe about 1 mm. long, concealed by the marcescent calyx, the body narrowly oblong in profile, incurved through about ½-circle, 2.5—3 cm. long, 5—6 mm. in diameter, fleshy, solid and subterete when first formed, in ripening becoming strongly compressed laterally, bicarinate by the prominent cordlike sutures, the faces low-convex, the thick, green but red-tinged, strigulose valves becoming leathery, brownish, rugulose-reticulate, inflexed below the short, cuspidate, unilocular beak as a complete septum; dehiscence apical, tardy, after falling; ovules 32-36; seeds about 3 mm. long, not seen fully ripe.
Distribution and Ecology - Gullied hillsides, in red clay and limestone gravel, preferring northern exposures in piñon-juniper forest, 5000-5500 feet, very local but forming colonies, known only from the Virgin-Colorado divide in the region of Mokiak Pass, northern Mohave County, Arizona.—Map. No. 60.—April to May.
Discussion:The close resemblance of the Pagumpa milk-vetch, A. ensiformis, to A. cibarius, emphasized by Jones in the places cited in the synonymy above, is no doubt more than coincidental and indicates a very real relationship which emphasis on the greatly dissimilar pods has obscured. Despite the similarity in habit, A. ensiformis may be recognized even in flower by its ascending rather than diffuse stems and by the looser racemes of 15-25 (not 4-14) slightly smaller flowers. The discovery of A. Minthorniae var. gracilior, which I subordinated at first to A. ensiformis, provided the clue to an even closer affinity in another, unexpected direction. The var. gracilior may be described loosely as combining the vesture of A. ensiformis with the growth-habit of A. Minthorniae. Shorn of the variety, A. ensiformis differs from the now relatively polymorphic A. Minthorniae in its shorter, weakly ascending stems, incurved and finally divergent or humistrate peduncles, and especially in the pendulous fruits which finally fall away with the disjointing pedicels. The pod of the Pagumpa milk-vetch is thickly fleshy when first fully formed, and its pendulous attitude is perhaps due more to the weight of the watery tissues than to any purposeful torsion of the pedicel supporting it. Since the gently incurved, blunt-edged fruits are not at all swordlike, the epithet ensiformis is poorly chosen. When fresh they are fleshy, with green pulp and reddish skin, resembling small, curved sausages hung out in a secund row along the axis of the raceme.
Arizona United States of America North America