Tufted or somewhat mounded, the divisions of the closely forking, cespitose caudex beset with a thatch of persistent leaf-stalks and terminating in obconic crowns of rosulate leaves and sessile flowers, the herbage densely silvery-strigose throughout with fine, lustrous, appressed and some few narrowly ascending hairs up to 1.2-2.5 (3.6) mm. long, the hairs sometimes spreading late in the season; stipules broadly ovate or oblong-obovate, 6—13 mm. long, often transversely corrugated, glabrous dorsally except at base, thinly ciliate; leaves (1) 1.5-10 (13) cm. long, usually dimorphic, those expanding with the flowers more shortly petioled and with shorter and broader leaflets than succeeding ones, the petioles slender, wiry, subpersistent, the leaflets obovate-cuneate to rhombic-obovate or narrowly oblanceolate, (3) 7-27 (37) mm. long, mostly acute or acuminate, more rarely obtuse, flat or loosely folded, dorsally carinate by the midrib, the terminal one usually a trifle longer than the lateral pair; peduncles obsolete or nearly so; racemes capitately 2 (rarely 1 or 3)-flowered, not elongating; bracts hyaline, lanceolate or broadly ovate-acuminate, when broad folded around the base of the calyx, 4.5-7.6 mm. long, commonly tridentate, the middle tooth often triangular-acuminate, the lateral ones shorter, either obtuse or acute, the margins entire or sharply denticulate, sometimes beset with a few minute processes; pedicels almost 0 up to 1.6 mm. long; bracteoles 0 (exceptionally a minute scale); calyx 9.3-20 mm. long, the subsymmetrically obconic disc 1.6-2 mm. deep, the membranous, narrowly cylindric or cylindro-ellipsoid tube 6.5-16 mm. long, 1.6-4.3 mm. in diameter, the firmer, subherbaceous teeth 1.6-4 mm. long, the whole becoming scarious, at first distended by the tumescent ovary, finally ruptured at base; petals commonly white (drying yellowish), the keel-tip pinkish-lilac, rarely all pink-purple or bluish, withering-persistent; banner nearly erect, oblanceolate or spatulate-oblanceolate, shallowly notched, 16-2S mm. long, 3-9.4 mm. wide; wings 12.2-24.2 mm. long, the claws 6.S-15.2 mm., the straight, narrowly oblong or oblong-oblanceolate, obtuse or obliquely emarginate blades 6-11.2 mm. long, 1.2-3.2 (3.6) mm. wide; keel 10.4-21.8 mm. long, the claws 6.7-15 mm., the obliquely elliptic or lunately half- elliptic blades 4-7.5 mm. long, 1.5-3 mm. wide, gently incurved through ± 45° to the bluntly triangular apex; anthers 0.65-0.95 (1.1) mm. long; pod erect, sessile (often concealed by imbricated stipules), subsymmetrically ovoid-ellipsoid, (6) 6.5—10 mm. long, 2.6—5 mm. in diameter, obtuse at base, contracted at apex into a short, erect or declined cusp, the body a trifle laterally compressed, obtusely carinate ventrally by the thick suture, sometimes obscurely sulcate or flattened dorsally at or just above the base, the somewhat fleshy, densely strigose-hirsutulous valves becoming leathers', not inflexed; seeds ochraceous, sometimes with a purple spot at the hilum, or deep purple-black, smooth but dull, sometimes distorted by crowding, 1.6—2 mm. long.—Collections: 77 (xv); representative: Breitling 15,955 (NY); Macoun & Herriott 70,480 (ND); C. L. Hitchcock 15,851 (NY. RSA), 16,216 (NY, RSA, WS), 16,308 (RSA, WS); Lunell in 1905, 1907, 1912 (NY); Rydberg 635 (NY); M. Ownbey 558 (NY, WS, WTU); C. L. Porter 6873 (NY); Ripley & Barneby 7SI8 (CAS. RSA, UTC).
Barren knolls, hilltops, and gullied badlands, on limestone, shale or sandstone, mostly below 5000 feet but ascending to 7000 feet in western Wyoming, widespread and locally plentiful, especially in actively eroded sites along water courses, southern Alberta to extreme southwestern Manitoba, south through North and South Dakota to western Nebraska, west in Montana to the upper Missouri and Madison Rivers and in Wyoming to the valleys of the North Platte and Wind Rivers; apparently isolated west of the Continental Divide in Summit County, Utah; reported (Jones, 1923) from northern Colorado.—Map No. 163.—Late April and May, into June at great elevations westward.
Astragalus gilviflorus (pale yellow-flowered, appropriate only to herbarium specimens) Sheld. in Minn. Bot. Stud. 1: 21. 1894, a substitute for A. triphyllus (three-leaved) Pursh, Fl. Amer. Sept. 2: 740. 1814 (non Pall., 1800).—"In Upper Louisiana, Bradbury."— Holotypus, labeled "Louisiana, Bradbury. Pursh’s specimens," PH (herb. Pursh.)! isotypi, BM, NY (frag, ex herb. Lambert.)!—Phaca triphylla (Pursh) Eat. & Wright, N. Amer. Bot. 351. 1840. Tragacantha triphylla (Pursh) O. Kze., Rev. Gen. 948. 1891. Orophaca triphylla (Pursh) Britt. in Britt. & Br., I11. Fl. 2: 306, fig. 2154. 1897.
Phaca caespitosa (tufted) Nutt., Gen. 2: 98. 1818.—" ... near the confluence of Sawanee River and the Missouri."—No spm. so labeled found at BM, K, NY, or PH; lectotypus, labeled by Nuttall "Phaca * caespitosa. Missouri.," GH!—This name, based at least in part on A. triphyllus Pursh, should perhaps be considered an illegitimate substitute for the preceding.— Non A. caespitosus Pall., 1800, nec Gray, 1864.
Phaca argophylla (silver-leaved) Nutt. ex T. & G., Fl. N. Amer. 1: 342. 1838.—"Summits of mountains on the upper waters of the Platte."—Holotypus, labeled by Nuttall "Phaca *argo- phylla. R. Mts. Platte.," BM! isotypus, K!-Non A. argophyllus Nutt. ex T. & G., 1838.—Orophaca argophylla (Nutt.) Rydb. ap. Britt., Man., Ed. 2. 1067. 1905, quoad nom. sol.
The plains orophaca, A. gilviflorus, the first and best-known species of its type, is rather variable in the shape of the leaflets and especially in the size of the flowers, but the taxonomist attempting to correlate the variable features and to explore through them the possibilities of racial differentiation is at a disadvantage because of the scarcity of flowering material in herbaria. The species is among the earliest spring flowers of its region, bursting into bloom with the first warm weather from buds formed apparently in winter. The blooming period is short and usually long past before professional collectors take to the field. So far as known the commonest, presumably typical phase of A. gilviflorus has narrowly oblanceolate leaflets (at least in mature leaves) and long, whitish flowers with calyx mostly 13-20 mm., a dorsally glabrous banner 20-28 mm., and a keel 15-22 mm. long. In western Montana (Custer, Lewis and Clark, Meagher, and Glacier Counties, probably elsewhere) plants with comparatively short flowers (calyx ± 9-10 mm., banner 16-18 mm., keel 10.5-12 mm. long) seem to be common, but I do not know whether these replace the ordinary sort. In some small-flowered plants the leaflets are comparatively short and broad in all leaves, but this is known to occur occasionally in combination with a long flower (= Phaca argophylla). The leaves of the plains orophaca are so often dimorphic, with longer petioles and leaflets in leaves produced after anthesis, that it is fair to regard this peculiarity as characteristic of the species. Other variants noticed in Montana by the observant collector C. Leo Hitchcock (the characters not always verified by me) are one with "corolla blue, the banner hairy on the back" (from Wheatland County, No 16,308) and another with "keel ciliate on the upper half’ (from Broadwater County, No. 15,886). On the upper Wind River in Wyoming, at elevations above normal for the species, some populations of A. gilviflorus are characterized by long, glabrous flowers varying from pale bluish-lilac to vivid pink-purple. All of these variants require and deserve attentive study.
The flowers on a plant of A. gilviflorus ordinarily bloom in rapid succession and last only for a few days, making a bright but fugitive display. As a rule only the neat lower leaves have reached full size at this time, and the long, narrow, glistening white flowers, which stand erect out of the crowns of silvery foliage, are wonderfully handsome. The plains orophaca can be grown with some difficulty in the eastern United States but is not long-lived under garden conditions, and moreover, its brief blossoming period does not recommend it. In summer, when the mature leaves have developed and the flowers have withered to papery tatters in the leaf- axils, even healthy plants take on an untidy, moribund appearance which is far from ornamental.