compressed-triquetrous with sharply carinate ventral and narrow but obtuse lateral angles, the almost flat lateral faces much broader than the narrowly or (at maturity) openly and deeply sulcate dorsal face, the thin, pale green, glabrous valves becoming papery, stramineous, somewhat lustrous, finely cross-reticulate, inflexed as a complete or nearly complete septum 1.2-2.5 mm. wide; seeds buff or olivaceous, often purple-speckled, lustrous but minutely pitted, 1.8-2.9 mm. long.—Collections: 40 (ii); representative: J. W. Thompson 11,442 (CAS, NY, RM, RSA, WS); Cronquist 6498 (ID, NY, TEX, WS); Ripley & Barneby 10,776 (CAS, RSA, WILLU).
Dunes and sandy barrens along the Columbia River and its immediate affluents, 250-1000 feet (reportedly up to 2350 feet in Gilliam County, Oregon), locally plentiful and rather common from Kittitas and Grant Counties, Washington, downstream to Gilliam County, Oregon, apparently most abundant between the mouths of the Yakima and Umatilla Rivers.—Map No. 153.—April to July.
Astragalus succumbens (lying down) Dougl. ex Hook., Fl. Bor.-Amer. 1: 151. 1831.—"On the barren grounds of the Columbia and near the Wallawallah River, North-West America. Douglas."—Holotypus, from "the junction of Wallahwallah River with the Columbia, 1826," K! isotypi, BM, GH (fragm.)! the spm. dated 1830 at G is perhaps also an isotypus!—Tragacantha succumbens (Dougl.) O. Kze., Rev. Gen. 948. 1891. Phaca succumbens (Dougl.) Piper in Contrib. U. S. Nat. Herb. 11 (Fl. Wash.): 370. 1906. Hamosa succumbens (Dougl.) Rydb. in Bull. Torr Club 54: 14. 1927.
The crouching milk-vetch, A. succumbens, is a plant of strong individuality and of great beauty when in flower. It is easily recognized by its low, rather coarse, distally zigzag stems, copious hirsute vesture, and long, ascending, sessile, compressed-triquetrous pods becoming straw-colored and glossy in the course of ripening. The flowers are remarkable for the exserted, apically dilated and (commonly) notched wings, which are either white or at least much paler than the roseate-purple banner. In relation to the pod’s size, the seeds are unexpectedly small.
The identity of A. dorycnioides, traditionally listed as a synonym of A. succumbens, is discussed in Appendix I.