Diffuse, rather slender, with a shortly forking or at length knotty caudex, villous throughout with fine, sinuous, ± entangled, together with longer, almost straight, widely spreading or ascending hairs up to 1-1.7 (2) mm. long, the herbage gray or canescent, the calyces more densely villous or villous-tomentose, the inflorescence commonly white-silky; stems numerous, prostrate or decumbent with ascending tips, (0.5) 1-3.5 (4) dm. long, together forming low tufts or loosely woven mats, all simple, or shortly spurred (rarely branched) at 1—3 nodes preceding the first peduncle; stipules thinly herbaceous becoming papery-membranous, lanceolate or lance-acuminate or -caudate, 2.5—7 mm. long, decurrent around half or less of the stem’s circumference; leaves 2.5-10 cm. long, the lower ones slender-petioled, the upper shortly so or subsessile, with (9) 15—25 (29) narrowly elliptic to elliptic-oblanceolate and acute, occasionally (in some or all leaves) oblong-obovate to oblanceolate and obtuse or obtuse and mucronulate, flat or loosely folded, often scattered leaflets 4-16 mm. long; peduncles erect or incurved- ascending, 3-10 cm. long, subpaniculately disposed in the distal axils; racemes (6) 12-30 (35)-flowered, the spreading flowers at early anthesis crowded into an ovoid or oblong head, the axis ± elongating, (1) 1.5—5 (7) cm. long in fruit, the fruiting raceme narrowly oblong-cylindric, often interrupted toward the base; bracts herbaceous becoming membranous, linear or linear-setaceous, 1.5—4.5 mm. long; pedicels at anthesis obconic, 0.2—0.4 mm. long, in fruit 0.3—0.8 mm. long; bracteoles 0; calyx (5) 5.6—8.3 mm. long, white-, or the teeth partly black- villous, the subsymmetric disc 0.4-0.8 (1) mm. deep, the submembranous, ovoid- campanulate tube (2.5) 3.1—4.5 mm. long, (2.4) 2.6—3.6 mm. in diameter, the narrowly subulate, often incurved, herbaceous teeth 2—4.2 mm. long, the whole becoming papery-membranous, marcescent, ruptured or not; petals whitish or sordid, often tinged (or the banner veined) with grayish-lavender, commonly marcescent about the forming fruit; banner recurved through ± 50°. ovate-cuneate, 7-11 (11.7) mm. long, 4.3-6.2 mm. wide; wings 6.2-9.2 (9.8) mm. long, the claws 2.7-4 mm., the obliquely elliptic or narrowly obovate, rarely lance-elliptic, obtuse, subacute, or obscurely emarginate, gently incurved blades (3.8) 4.1-6.2 mm. long, 1.5-2.6 mm. wide, the left one usually concave and folded over the keel; keel 5.2-7.4 mm. long, the claws 2.5-3.7 (4.4) mm., the half-circular or -obovate blades 2.2-3.2 (3.8) mm. long, 1.6-2.2 mm. wide, abruptly incurved through 95-120° to the obtuse, sometimes obscurely porrect apex; anthers 0.30.5 (0.6) mm. long; pod horizontally spreading or widely ascending, sessile or elevated on a minute neck up to 0.3 mm. long, subpersistent on the receptacle, the body obliquely ovoid, (3.5) 4-6 mm. long, 2.5-3.5 mm. in diameter, abruptly cuspidate at apex, laterally compressed with plumply distended and convex lateral faces, keeled ventrally by the prominent, thick suture, shallowly sulcate dorsally but the groove open only near the base or sometimes subobsolete, the stiffly papery, densely villous-tomentulose valves inflexed as a complete septum produced into the pod’s apex; dehiscence tardy, after falling; ovules 4-8, rarely 9-10; seeds olivaceous, sometimes purple-speckled, smooth and sublustrous, 1.8-2.6 mm. long.—Collections: 54 (iv); representative: H. T. Rogers 668 (CAS, NY, WIS, WS, WTU); J. W. Thompson 11,663 (CAS, NY, WTU); Ripley & Barneby 10,773 (CAS, NY, RSA, WTU); Cronquist 6508 (ID, NY, SMU, TEX, WS); Cusick 1701 (ND, WS).
Dry hillsides, valley floors, in bunchgrass prairies and sagebrush scabland, commonly in sandy or sandy loam soils derived from basalt, 1000-2600, rarely up to 3900 feet, widespread and rather common in transmontane Washington, from Grand Coulee south and east to the lower Yakima River, the lower Umatilla Valley in northeastern Oregon, and the Clearwater Valley in eastcentral Idaho; apparently somewhat isolated on the upper Powder River in central Baker County, Oregon.—Map No. 156.—May to July.
Astragalus Spaldingii (Henry Harmon Spalding, 1804—1874, missionary and founder of Lapwai Mission near the mouth of the Clearwater River; his collections are believed to have been made by Mrs. Spalding) Gray in Proc. Amer. Acad. 6: 524. 1865, a substitute for A. chaetodon (with bristlelike calyx-teeth) Torr. ex Gray in op. cit. 6: 194. 1864 (non A. chaetodon Bge., 1851).—"Plains on the Kooskooskie River, interior of Washington Territory, Rev. Mr. Spalding, Dr. Pickering."—Holotypus, labeled "A. chaetodon Torr. ined. Kooskooskee. Mr. Spalding," NY! isotypi, GH, PH!—Tragacantha Spaldingii (Gray) O. Kze., Rev. Gen. 948. 1891. Phaca Spaldingii (Gray) Piper in Contrib. U. S. Nat. Herb. 11 (Fl. Wash.): 370. 1906.
The Spalding milk-vetch is easily recognized by its ovoid or finally oblong-cylindric, spikelike racemes of small, crowded, pallid flowers which give rise to tiny, densely pubescent, ovoid pods invested for at least three fourths and often their whole length by the somewhat accrescent calyx. As the fruit reaches maturity, the pedicels disjoint readily, and the calyx, marcescent petals, and pod fall together to the ground. Small and light, they are quickly carried away by the wind and may sometimes be found piled up in miniature windrows under tufts of grass or among the twigs of desert shrubs. Dehiscence is delayed until after falling, and it is uncertain how the seeds are finally released, or even whether the pod itself disjoints naturally from the receptacle as in other members of the section. Enclosed and supported as it is by the enveloping calyx, the pod can hardly be subjected to the mechanical stresses which are responsible for the fracture of the joint in most piptoloboid astragali.
The plants of the Spalding milk-vetch are often browsed and are said to provide good forage, being eaten greedily by stock and horses (Pickett 537, WS).