Astragalus Paysonii

  • Title

    Astragalus Paysonii

  • Author(s)

    Rupert C. Barneby

  • Scientific Name

    Astragalus paysonii (Rydb.) Barneby

  • Description

    123. Astragalus Paysonii

    Rather slender perennial, with a taproot and shortly forking caudex, appearing glabrous but the stems, lower surface of the leaflets, and the ovary and pod thinly strigulose with fine, straight, appressed or narrowly ascending hairs up to 0.4-0.6 mm. long, the thin-textured leaflets bicolored, bright green above, pallid and subglaucescent beneath; stems several or numerous, sometimes forming "large clumps," decumbent and ascending, 2-4.5 dm. long, simple or spurred at 1-2 nodes preceding the first peduncle; stipules submembraneous becoming papery, 2-5 mm. long, the lowest ovate-triangular, decurrent around ± ½ the stem’s circumference, the upper ones lanceolate or lance-acuminate, more shortly cauline, commonly reflexed; leaves 4-9.5 cm. long, all petioled but the upper ones very shordy so or subsessile, with 7-15 (17) ovate, ovate-oblong, or obovate-cuneate, mostly retuse, flat leaflets 5-20 mm. long; peduncles slender, incurved-ascending, 3-9cm. long; racemes at first rather closely 5-20-flowered, the flowers ascending and early declined, the axis somewhat elongating, 1-4.5 cm. long in fruit; bracts membranous, ovate or lanceolate, 0.8-2 mm. long; pedicels at anthesis 0.5-0.7 mm. long, in fruit arched outward, somewhat thickened, 1-1.2 mm. long; bracteoles 0; calyx 3.2-4.6 mm. long, densely strigulose with black or black and white hairs, the subsymmetric disc 0.6-0.8 mm. deep, the campanulate tube 2-2.9 mm. long, 2-2.5 mm. in diameter, the triangular-subulate teeth 1-1.7 mm. long, the whole becoming papery, marcescent; petals whitish, apparently sometimes faintly lilac-tinged; banner recurved through 45°, ovate-cuneate, retuse, 7-9 mm. long, 5.2-5.6 mm. wide; wings 6.4-7.8 mm. long, the claws 2-2.6 mm., the oblong- obovate, obtuse, moderately incurved blades 4.9-5.8 mm. long, 2-2.5 mm. wide; keel 4,8-5.5 mm. long, the claws 2-2.5 mm., the half-obovate blades 3.1-3.3 mm. long, ± 2 mm. wide, incurved through 115-130° to the bluntly deltoid, obscurely porrect apex; anthers 0.3-0.45 mm. long; pod pendulous (or widely spreading from horizontal peduncles), stipitate, the stipe 1-1.5 mm. long, concealed by the calyx, the lunately linear-ellipsoid body 1-1.7 cm. long, 2.5-3.5 mm. in diameter, cuneately contracted at both ends, at apex into a straight, subulate cusp 1-1.5 mm. long, triquetrously compressed, with low-convex lateral and deeply but narrowly sulcate dorsal faces, carinate ventrally by the thick, straight or gently concave suture, the thin, greenish-stramineous, thinly strigulose valves becoming papery, stramineous or brownish, cross-reticulate, inflexed as a complete septum 1.3—2 mm. wide; dehiscence apical, tardy; ovules 8—10; seeds (little known) brown, smooth, 1.9—2.1 mm. long.—Collections: 3 (o); representative: Christ 18,183 (ID, RSA); R. J. Davis s. n. (RSA).

    Open places in the timber belt, sometimes in burned-over forest, on decomposed granites, rare and local, known only from the Green-Snake River watershed in Sublette County, Wyoming (west of Merna), and from the Clearwater Mountains (4 miles east of Red River Ranger Station; Indian Hill), Idaho County, northcentral Idaho.—Map No. 50.—July to October.

    Astragalus Paysonii (Rydb.) Barneby in Leafl. West. Bot. 4: 60. 1944, based on Hamosa Paysonii (Edwin Blake Payson, 1893-1927, professor of botany at RM) Rydb. in Bull. Torr. Club 54: 22. 1927.—‘Type collected at Horse Creek, seven miles west of Merna, Sublette County, Wyoming, Payson & Payson 2748 — "—Holotypus, collected July 18, 1922, NY! isotypi, GH, MO, US!

    Despite the great distance between the two areas from which the Payson milk-vetch is known at present, the material is essentially uniform and certainly conspecific. Intermediate stations must be expected to appear, as the great mountain wilderness of western Wyoming is more thoroughly explored botanically. No close floristic relationship is known to exist between the Clearwater Mountains and those of the Tetons and adjoining ranges in Wyoming, but there are several interesting links between the floras of the Oregon Coast Ranges and the Clearwaters. In the sectional key A. Paysonii has been contrasted with a small-flowered Mexican species, but its nearest relative is probably the cismontane A. umbraticus from which it is distinguished by its fewer leaflets, tiny flowers, and few-ovulate, puberulent pod. Little is known of the ecology of the Payson milk-vetch. It was originally discovered in burned-over spruce and fir forest, a circumstance which recalls the preference of some cismontane Miselli, notably A. Congdoni and A. agnicidus, for a disturbed habitat. In Idaho it was found by R. J. Davis (personal comm.) in openings of Douglas fir forest, in moderately moist soil at about 7200 feet, a habitat similar to that favored by A. umbraticus, even though at much greater altitude. Everything points to a common origin with the white-flowered cismontane species of the section.