Monographs Details: Astragalus nuttallianus var. zapatanus 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:

333i. Astragalus Nuttallianus var. zapatanus

Usually very slender, the prostrate, radiating stems up to 3 dm. long and probably longer, hirsutulous with rather stiff, loosely ascending and incurved hairs up to 0.4-0.75 mm. long, the leaflets green or greenish, thinly pubescent to glabrous above; leaves 1.5-4.5 (5) cm. long, the (7) 9-17 narrowly cuneate to oblong, oval, or oblong-cuneate, retuse or deeply emarginate leaflets 2-7 (8) mm. long; peduncles more or less dimorphic, the early ones (sometimes all) filiform, (2) 5-17 mm. long, 1-2-flowered, the later ones sometimes up to 4.5 cm. long and up to 4-flowered, the racemes subcapitate; calyx 3-4.6 mm. long, pilosulous, the tube 1.6-2.7 mm. long, 1.5-2.1 mm. in diameter, the teeth 1.2-1.9 mm. long; petals whitish faintly lavender-tinged, or the banner broadly edged with bluish-lilac and striate; banner (4) 4.9-6.7 mm. long; wings (4) 4.8-6.3 mm. long; keel not more than 0.7 mm. shorter than the banner, 3.9-6 mm. long, the claws 1.7-2.4 mm., the obliquely triangular blades 2.3-3.8 mm. long, incurved through 75-90° to the sharply triangular, slightly porrect apex; pod 1.3-1.8 cm. long, 2.6-3.2 mm. in diameter, very slightly and evenly incurved, pilosulous with ascending or subappressed hairs up to 0.4-0.5 mm. long, fully bilocular; ovules 10-16.—Collections: 7 (ii); representative: Shinners 17,665 (SMU); B. L. Turner 4504 (TEX); LeSueur 215 (TEX); Ripley & Barneby 9034, 9055 (RSA); C. & A. Lundell 15,051 (NY).

Dry sandy fields, roadsides, and waste places or abandoned gardens, locally abundant in the lower Rio Grande Valley from near Laredo, Texas, southeast to the Gulf Coast in northern Tamaulipas.—Map No. 149.—February and March.

Astragalus Nuttallianus var. zapatanus (of Zapata County, Texas) Barneby in Field & Lab. 24 : 36. 1956.—"... Texas. Webb. Co.: Laredo, March 15, 1917, E. J. Palmer 11289 ... Holotypus, NY!

The var. zapatanus suggests a delicate, prostrate phase of var. trichocarpus, differing in its generally looser vesture of incurved hairs and in the truncate-emarginate leaflets of all, even the uppermost leaves. It forms extensive colonies of homomorphic individuals and is apparently the dominant small-flowered milk-vetch on the sands of Jim Hogg and Zapata Counties, occurring even as a weed in the courthouse square in Hebbronville and along roadsides thereabouts. The early peduncles are short, slender, and mostly 1-flowered; this is a juvenile character, not always perpetuated upward along the stems, the 2—4-flowered, longer-pedunculate, later racemes being hardly different from those of var. trichocarpus. While young plants of var. zapatanus superficially resemble A. nyensis, a piptoloboid annual of southern Nevada, the relationship is not at all close. Truly ripe fruits of var. zapatanus are still required to show the manner of fall and dehiscence.