Monographs Details: Astragalus emoryanus (Rydb.) Cory
Authors:Rupert C. Barneby
Authority: Barneby, Rupert C. 1964. Atlas of North American Astragalus. Mem. New York Bot. Gard. 13(2): 597-1188.
Family:Fabaceae
Discussion:

323.  Astragalus Emoryanus

Annual or winter-annual, exceptionally persisting into a second year, diffuse or prostrate, densely to quite thinly strigulose, hirsutulous, or subvillosulous with appressed, incurved-ascending, or more rarely rather stiffly spreading hairs up to 0.5-0.75 (1.05) mm. long, the herbage silvery-cinereous or sometimes greenish, the leaflets commonly pubescent on both sides, but sometimes only marginally or quite glabrous above; stems 3-several or very numerous, radiating from the root-crown, (0.25) 0.4-4.5 (6) dm. long, branched or spurred below, floriferous upward from near or below the middle, together forming loosely or quite densely woven mats; stipules 1.5-3.5 (5.5) mm. long, deltoid, ovate, or triangular, membranous or membranous-margined, subglabrous dorsally, semi- or the lowest sometimes almost fully amplexicaul; leaves 1-4.5 (8) cm. long, all shortly petioled or the uppermost subsessile, with (7) 11-19 (21) often rather crowded, oval-obovate, obcordate, broadly cuneate-oblanceolate, or sometimes mostly elliptic-oblanceolate, obtuse or retuse, loosely folded or flat leaflets 2-10 (14) mm. long; peduncles slender, mostly (1) 2-6 (10) cm. long and as long or longer than the leaf, but some early ones (or exceptionally all) much shorter and few-flowered; racemes shortly but loosely (1) 2-10 (12)-flowered, the flowers spreading or finally declined, the axis little elongating, (0) 0.3-2.5 (3.5) cm. long in fruit; bracts submembranous, ovate or lanceolate, 0.5-1.8 mm. long; pedicels at anthesis ascending, (0.5) 0.7-1.8 mm. long, in fruit arched outward, a little thickened, (0.6) 1-2 mm. long; bracteoles 0 (exceptionally a minute scale); calyx 3.6-6 mm. long, pubescent like the herbage with white, mixed black and white, or nearly all black hairs, the subsymmetric disc (0.4) 0.5-1.1 mm. deep, the membranous, pallid or purplish, campanulate tube 1.9-3.5 mm. long, (1.5) 1.7-2.5 (2.8) mm. in diameter, the subulate or lance-subulate teeth 1.3-2.5 (2.9) mm. long; petals pink-purple, the banner with a large, pallid, striate eye in the fold; banner recurved through ± 45°, obovate-, ovate-cuneate, or flabellate, widely and sometimes deeply notched, (6) 7.3-11.2 mm. long, (3.1) 5.3-9.5 mm. wide; wings (5.1) 6.2-8.8 (10) mm. long, the claws (1.8) 2-3 mm., the oblong-oblanceolate, -obovate, or narrowly oblong, obtuse or obscurely emarginate blades (3.2) 3.7-6.6 (8) mm. long, (1.1) 1.7-3.4 mm. wide; keel (4.5) 4.8-6.6 mm. long, the claws (1.9) 2.2-3.3 mm., the half-obovate or -circular blades (2.3) 2.6-3.6 (4) mm. long, (1.5) 1.9—2.5 mm. wide, rather abruptly incurved through 90-100° to the bluntly deltoid apex; anthers (0.25) 0.3—0.5 mm. long; pod spreading, declined, or (when humistrate) ascending, linear-oblong or narrowly lance-oblong in profile, incurved gently and evenly through ¼-½ circle or (when short) lunately incurved to almost straight, 0.8-2.2 cm. long, (2) 2.2-4.3 mm. in diameter, obtuse at base, shortly cuspidate at apex, triquetrously compressed with low-convex lateral and openly sulcate dorsal faces, the green or purple-tinged, glabrous valves becoming papery, pale brown or stramineous, delicately reticulate, inflexed as a complete or nearly complete septum 1.2-2 mm. wide; ovules (8) 10-15 (17); seeds compressed-quadrangular, brown or olivaceous sometimes dotted with purple, smooth or somewhat pitted, (1.8) 2-2.9 mm. long.

The Emory milk-vetch is the only species of its subsection known to occur east and south of the Colorado River; it is confined (except for outposts in northwestern Arizona) to New Mexico, Texas, and northern Mexico, where it can be confused only with the small-flowered genuine Leptocarpi, A. leptocarpus itself, and forms of A. Nuttallianus with glabrous ovary and fruit These are distinguished ideally by their persistent pods which turns black on drying, and at anthesis, in most instances, by the triangular-acute keel-tip, the hispid-ciliate calyx-teeth, or leaflets of some leaves elliptic and subacute, not all truncate-retuse. Only some phases of A. Nuttallianus var. macilentus found on the Edwards Plateau in westcentral Texas have all these points in common with A. Emory anus, and it is only in this comparatively small area that well-formed pods, showing the characteristic incipient stipe of var. macilentus or the rounded base of the present species, are required for identification.

Notable features of A. Emoryanus are its wide climatic tolerance, apparent indifference to type of bedrock, and pattern of dispersal very largely confined to the valley of the Rio Grande, along which it descends from nearly 7000 feet elevation near Albuquerque to the Gulf Coast. In all probability the foregoing description conceals several distinguishable geographic races, but only one of them, strongly marked by an abrupt shortening of the pod analogous to that found in A. Pringlei as compared with A. nothoxys, stands out with sufficient clarity to deserve recognition for the present.