Monographs Details: Astragalus nuttallianus var. trichocarpus Torr. & A.Gray
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:

333e. Astragalus Nuttallianus var. trichocarpus

Somewhat intermediate between the preceding and the following varieties, but with smaller flowers than var. pleianthus and pubescent pod, the hairs mostly longer than in var. austrinus and incurved-ascending, up to 0.5-1 mm. long; leaflets mostly 11-13 and broadly elliptic, exceptionally emarginate in some lower leaves; racemes (1) 3-6-flowered; banner (4) 5-7 mm., keel (as in the preceding) mostly 4-5 mm. long.—Collections: 53 (iii); representative: all at SMU & TEX annotated by me as A. Nuttallianus var. trichocarpus 8; Lindheimer 748 (NY); Tracy 9109 (MO, NY, TEX, WIS); A. Heller 1380 (NY, WS).

Habitats of the preceding, and of almost coextensive range in eastern Texas, most abundant on and near the Balcones Escarpment and Gulf Coastal Plain, extending to the coast between Matagorda Bay and Corpus Christi, north, becoming less frequent, almost to the Red River, passing west into var. austrinus west from central Edwards Plateau.—Map No. 149.—March to May.

Astragalus Nuttallianus var. (ß) trichocarpus (with hairy pods) T. & G., Fl. N. Amer. 1: 333. 1838.—"Texas, Drummond!"—Holotypus, from Drummond’s Collection I, NY! isotypi, some dated "1833," others "1834," BM, G, OXF!—A. trichocarpus T. & G. ex M. J. Young, Fam. Less. Bot. with Fl. Tex. 228, 1873, probably an inadvertent comb., due to faulty copying from Fl. N. Amer. (non Grah. ex Bth. in Royle, I11. Himal. 199. 1835).

The var. trichocarpus is taken up in a sense much more restricted than was foreseen in my naive note (1942, p. 109) on the western varieties of A. Nuttallianus, where my concept, derived from Rydberg, was substantially equivalent to var. austrinus of these pages but included the bilocular element of var. imperfectus. The name is here more narrowly applied to those eastern and central Texan forms of small-flowered milk-vetch that differ from sympatric varieties in their pubescent ovaries, and from the forms of var. austrinus with strigulose pods, found mostly at higher elevations from western Texas westward and southward, in the longer and looser vesture of the ripe fruit, the commonly more robust and leafy growth-habit, and mostly broader and slightly more numerous leaflets to the average leaf. The meridian drawn through San Angelo, Texas, approximately coincides with the west limit of var. trichocarpus, while typical var. austrinus (except for isolated records in southern Texas noted below as probable introductions of recent date) extends only rarely and for no great distance east of this line. As might be expected, the two varieties are not clearly distinguished where their ranges of dispersal overlap. The holotypus of var. trichocarpus is not the extreme phase of its sort, the hairs on the pod being subappressed and only just 0.5 mm. long. Its exact point of origin is not recorded, but it is most closely matched by modern collections from eastcentral Texas. As already implied, var. trichocarpus as redefined formed part of Hamosa austrina sensu Rydberg (1927, p. 329; 1929, p. 431) and of var. austrinus as accepted by Shinners (in Field & Lab. 25: 33. 1957).