Astragalus pinonis

  • Title

    Astragalus pinonis

  • Authors

    Rupert C. Barneby

  • Scientific Name

    Astragalus pinonis M.E.Jones

  • Description

    55. Astragalus pinonis

    Astragalus pinonis Usually slender, weak, few-stemmed, sparsely leafy, strigulose throughout with straight or nearly straight, appressed hairs up to 0.2—0.5 mm. long, the herbage gray or greenish-cinereous, the leaflets pubescent on both sides but bicolored, yellowish-green beneath the vesture above; stems solitary or 2-4 (5), arising from the root-crown shortly below soil-level, in open places erect or straggling but commonly supported by sagebrush, (1) 1.5—6 dm. long, leafless and purplish in the lower 1/3, either simple or bearing divaricate branches at the first few leaf-bearing nodes, usually zigzag distally; stipules 1.5—5 mm. long, dimorphic, the lowest ovate, obtuse, papery, chestnut-purple, adnate to the vestigial petiole and decurrent-am- plexicaul around 1/2-2/3 the stem’s circumference, the upper ones herbaceous, small, deltoid or triangular-subulate, sometimes deflexed; leaves usually divaricate, 2-8 (11) cm. long, the uppermost subsessile, with 9-15 (19) linear to linear- oblong or -oblanceolate, obtuse or retuse leaflets (2) 4-16 (19) mm. long; peduncles either divaricate or widely incurved-ascending, (1.5) 3—8 cm. long; racemes loosely 5-19-flowered, the axis somewhat elongating, 2-7 cm. long in fruit; bracts membranous, pallid or purplish, ovate or ovate-acuminate, 1-2 mm. long; pedicels at anthesis 1-2 mm. long, in fruit arched outward, thickened, (1.5) 2-3 mm. long; bracteoles 0 (rarely a minute scale); calyx 4.3-5.6 mm. long, strigulose with black, white, or mixed black and white hairs, the subsymmetric disc 0.8-1.3 mm. deep, the campanulate tube 2.3-3.8 mm. long, 2.5-3.3 mm. in diameter, the broadly subulate teeth 1-2 mm. long, the ventral pair often broadest; petals greenish-white or sordidly ochroleucous, commonly tinged distally, and the banner veined, with dull lilac; banner suborbicular-cuneate, emarginate, 8.2-10.3 mm. long, 7-9 mm. wide; wings 8-9.8 mm. long, the claws 3-3.8 mm., the broadly and obliquely obovate or broadly oblanceolate, obtuse or erose-emarginate blades 5.1-6.6 mm. long, 2.3-3 mm. wide; keel 7.5-9.7 mm. long, the claws 3.1-4 mm., the blades 4.8-6.2 mm. long; anthers 0.6-0.7 mm. long; pod spreading or loosely declined; subsessile or elevated on an obscure, glabrous, stipelike neck up to 1 mm. long, the body narrowly oblong-ellipsoid, straight or a trifle incurved, 2-3.5 cm. long, 5.5 8.5 mm. in diameter, cuneate at base, abruptly acute and cuspidate at apex, terete or a little dorsiventrally compressed, obtusely carinate by the thick, prominent sutures, the somewhat fleshy, brown- or purple-tinged, densely strigulose valves becoming stiffly papery, brownish-stramineous and coarsely reticulate; dehiscence apical and downward through the ventral suture; ovules (19-20) 32-42; seeds (seldom seen) brown, smooth, ±1.7 mm. long (probably sometimes longer).— Collections: 17 (viii); representative: Maguire & Holmgren 25,528 (CAS, NY, RSA, UTC, US, WS); Ripley & Barneby 6333 (CAS, RSA), 6260, 6271, 6304 (RSA).

    Dry hillsides and valley floors, in stiff or loose, sandy clay soils derived from limestone, nearly always taking shelter under and scrambling up through low sagebrush, more rarely on open slopes with piñon and juniper, 5200-7400 (reportedly 8000) feet, uncommon and nowhere abundant, eastcentral Nevada (White Pine Mountains south to the Quinn Canyon and Highland Ranges, White Pine, northwestern Nye and northern Lincoln Counties) and western Utah (Frisco Mountain, central Beaver County; Tintic, western Juab County); apparently also in the foothills of the Kaibab Plateau, Coconino County, Arizona.—Map No. 25.— May to July.

    Astragalus pinonis (of the piñon or nut pine) Jones, Contrib. West. Bot. 8: 14. 1898 ("Pinonis").—"Frisco, Utah, June 22, 1880, at about 8000 ft. alt... "—Holotypus, dated 1888, POM!—Pisophaca pinonis (Jones) Rydb. in N. Amer. Fl. 24: 325. 1929.

    The piñon milk-vetch is widely dispersed through the limestone mountains of eastern Nevada, but it is a relatively rare astragalus nevertheless, found usually in small, scattered colonies. The apparent scarceness of individuals may be due, in part, to the inconspicuous nature of the plants and their habit of growing up through twiggy entanglements of low sagebrush (Artemisia arbuscula), by which all but the racemes of small, pallid or faintly lilac-tinged flowers and the narrow spindles of the fruit are concealed from view. The species was known to Jones (1923, p. 196, Pl. 44) and to Rydberg (1929, p. 325) only from meager material from Utah, the two collections from which Jones drew the original description in 1898; it was mistakenly referred to sect. Flexuosi or Pisophaca (= our sect. Scytocarpi) on account of the narrow subterete unilocular pod. Jones voiced a suspicion that when better known it might prove to belong in sect. Lonchocarpi, of which it is now known to have all important features.

    Two collections from Arizona (South Canyon, south of House Rock Valley, Coconino County, Goodding 92-49, ARIZ, CAS; Kaibab Forest, B. Swapp 37, BRY) have been identified tentatively as A. pinonis, but possibly represent an allied species or a distinct variety. The first has flowers only, the second no more than one pod, of which the compression is not clear. The terminal leaflets of some leaves are continuous with the rachis, and in Goodding’s plant the ovules are only 19-20 in contrast to 32-42 characteristic of the Nevada plant. The flower is apparently that of subsect. Aequales, with beaklike keel-tip. More material is required.