Monographs Details: Astragalus nuttallianus var. pleianthus (Shinners) Barneby
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:

333d. Astragalus Nuttallianus var. pleianthus

Variable in stature but usually vigorous and leafy, strigulose or hirsutulous with subappressed or ascending, mostly straight, lustrous hairs up to 0.65-1.35 mm. long, cinereous or greenish, the leaflets pubescent on both sides, sometimes thinly so, very rarely glabrous above; stems mostly 1-3 (4.5) dm. long; leaves 1-6.5 (8) cm. long, with 13-17 (21) rather broadly elliptic leaflets 2-13 (15) mm. long, those of the upper leaves subacute or obtuse, those of the lower ones obtuse or emarginate; peduncles either longer or (the earlier ones especially) shorter than the leaf; racemes subcapitately 4-9 (12)-flowered, the axis not or scarcely elongating, up to 8 (12) mm. long in fruit; calyx mostly 4-5.4 (5.7) mm. long, hirsute or hirsutulous with rather stiff, straight, lustrous (white or partly black or fuscous) hairs up to (0.6) 0.65-1.2 mm. long, the tube 2-3.1 mm., the teeth mostly 1.8-2.8 (3.1) mm. long; petals purple, the banner with a large, whitish eye; banner suborbicular-cuneate, mostly 7-9 (9.5) mm. long; keel mostly 5-6.6 mm. long, the blades lunately half-elliptic, incurved through 50-90° to the triangular, acute or subacute, nearly always porrect apex; pod sessile or contracted at base into an obscure stipelike neck up to 0.5 mm. long, mostly 1.3-2.4 cm. long, 1.8-2.8 (3) mm. in diameter, arched most strongly near the base and straight or nearly so thereafter, the valves glabrous, inflexed as a complete septum 0.9-2 mm. wide; ovules 14-18 (20).—Collections: 52 (iii); representative: mentioned below.

Prairies, roadsides, and open woodlands, mostly below 1500 feet, locally abundant and rather common in central and southeastern Texas, extending west to Edwards Plateau in Sutton County, south (but less common) to the Coastal Plain in Refugio County, north (becoming rarer) nearly to the Red River.— Map No. 149.—March to May.

Astragalus Nuttallianus var. pleianthus (Shinners), comb. nov., based on A. austrinus var. pleianthus (with more and larger flowers) Shinners in Field & Lab. 25: 33. 1957.—"5.7 miles south-southeast of Richland, Navarro Co. [Texas], Shinners 22,900, 28 April, 1956 ... "—Holotypus, SMU, not examined; isotypus, GH!

With var. pleianthus I begin to take up the forms of small-flowered milk-vetch with sub- capitate racemes, acute keel-tip, and at least some leaflets rounded or acute and not truncate- emarginate at apex. Over the greater part of its range var. pleianthus is sympatric and often directly associated with var. Nuttallianus, var. trichocarpus, and the blunt-keeled var. macilentus. It resembles var. Nuttallianus in the glabrous pod but is easily distinguished by the shape of the nearly always more densely pubescent leaflets, hirsute or hirsutulous calyx, and decidedly larger flowers. It is apparently more closely related to var. trichocarpus, the hairy legume of which is the most convenient (although in the context unimportant) differential character, but the flowers of var. trichocarpus are also, at least on the average, smaller and fewer and the petals tend to be paler in coloring. Along its west edge the range of var. pleianthus overlaps that of the smaller-flowered var. austrinus, in which the pod varies from glabrous to strigulose; but the form with glabrous fruit has not been recorded from so far east. My concept of var. pleianthus is embodied in the extensive series of specimens built up by Dr. Shinners at SMU and the scarcely less important series at TEX; they were annotated during my preliminary studies of the complex as A. Nuttallianus var. trichocarpus ?.