Low tufted perennial pubescent herbs, with pinnately 3-7-foliolate leaves, the linear persistent leaflets firm in texture, spinulose-tipped. Flowers 2 to 4 together in the axils or solitary, nearly sessile, yellow or yellowish. Calyx campanulate, the teeth nearly equal. Keel obtuse, shorter than the wings. Ovary few-ovuled. Pod short, ovate, 1-celled, somewhat coriaceous, with 1 or 2 seeds. [Greek, referring to the sharp-tipped leaflets.]

About 5 species, natives of central North America, the following typical.

1. Kentrophyta Montàna Nutt. Prickly Milk Vetch

Fig. 2558

Kentrophyta montana Nutt.; T. & G. Fl. N. A. 1: 353. 1838. Kentrophyta viridis Nutt.; T. & G. Fl. N. A. 1: 353. 1838. Astragalus Kentrophyta A. Gray, Proc. Acad. Phil. 1863:

60. 1863. Homalobus montanus Britton, in Britt. & Brown, 111. Fl. 2:

306. 1897.

Densely tufted, intricately branched, 2'-10' high, finely canescent. Stipules linear-lanceolate, spiny-tipped, 2."-5" long; leaflets 3-7, linear, rigid, spiny, widely spreading, 3"-6" long, 1/2" wide; flowers 1-4 together in the axils, nearly sessile, yellowish-white or bluish-tinged, 2 -3" long; pod sessile or very short-stalked, 1-3-seeded, ovoid-oblong, acute, coriaceous, dehiscent, pubescent, 3"-4" long.

In dry, rocky places, South Dakota to Nebraska, New Mexico and Saskatchewan. June-Sept.

30. ORÓPHACA Britton, in Britton & Brown, 1ll. Fl. 2: 306. 1897.

Perennial, silvery or villous-pubescent low tufted herbs, with branched woody caudices, deep roots, membranous scarious stipules, sheathing and united below, and digitately 3-folio-late (rarely 5-foliolate) leaves, resembling those of Lupines. Flowers few, capitate or racemose, the clusters sessile or peduncled. Keel of the corolla blunt. Pod coriaceous, completely I-celled, ovoid or oval, few-seeded, villous, partly or wholly enclosed by the calyx. [Greek, mountain vetch.]

Three known species, the following, and one in Colorado and Wyoming. Type species: Oro-phaca caespitosa (Nutt.) Britton.

1. Orophaca Caespitósa (Nutt.) Britton. Sessile-Flowered Milk Vetch

Fig. 2559

Astragalus triphyllus Pursh, Fl. Am. Sept. 740. 1814. Not Pall. 1800. Phaca caespitosa Nutt. Gen. 2: 98. 1818. Orophaca caespitosa Britton, in Britt. & Brown, 1ll. Fl. 2:

306. 1897.

Silvery-canescent, densely tufted from a deep root, 2'-4' high. Stipules scarious, imbricated, glabrous, ovate-lanceolate, 3"-4" long; leaves digitately 3-5-foliolate, slender-petioled; leaflets oblong or oblanceolate, acute or obtusish at the apex, narrowed or cuneate at the base, 6"-8" long; flowers yellowish, 6"-8" long, sessile in the axils of the leaves; calyx-teeth half as long as the tube; corolla glabrous; pod I-celled, sessile, ovoid, acute or acuminate, coriaceous, dehiscent, villous-pubescent, enclosed by the calyx, 2"-3" long.

Plains and hills, Kansas, Nebraska and South Dakota to Montana and Saskatchewan. May-July.

2. Orophaca Argophýlla (Nutt.) Rydb. Silvery Milk Vetch

Fig. 2560

Phaca argophylla Nutt.; T. & G. Fl. N. A. 1: 342. 1838.

Astragalus hyalinus M. E. Jones, Proc. Cal. Acad. II. 5: 648. 1895.

Orophaca argophylla Rydb. in Britton, Man. Ed. 2, 1067. 1905.

Similar to the preceding species, but the leaflets relatively shorter and broader. Stipules scarious; corolla about 5" long, pubescent outside; calyx-teeth a little shorter than the tube.

In dry soil, Nebraska and Wyoming. May-July.

3. Orophaca Sericea (Nutt.) Britton. Hoary Milk Vetch

Fig. 2561

Phaca sericea Nutt.; T. & G. Fl. N. A. 1: 343. 1838.

Astragalus sericoleucus A. Gray, Am. Journ. Sci. (II.) 33: 410. 1862.

Orophaca sericea Britton, in Britt. & Brown, 1ll. Fl. 2: 307. 1897.

Villous-pubescent, densely tufted, and spreading on the ground from a deep root, the stems 3-4' long. Leaves short-petioled, 3-foliolate; leaflets oblong or oblanceolate, acute or obtusish at the apex, narrowed or cuneate at the base, 2"-5" long; peduncles slender, 2-6-flowered, equalling or exceeding the leaves; flowers bluish-purple, about 3" long; pod I-celled, sessile, ovoid-oblong, coriaceous, acute, villous-pubescent, about 3" long, partly enclosed by the calyx.

In dry, sandy or rocky places, Nebraska to Wyoming and Colorado. May-July.