Monographs Details: Astragalus proimanthus Barneby
Authors:Rupert C. Barneby
Authority: Barneby, Rupert C. 1964. Atlas of North American Astragalus. Mem. New York Bot. Gard. 13(2): 597-1188.
Family:Fabaceae
Discussion:

367.  Astragalus proimanthus

Densely cespitose or pulvinate, the branches of the repeatedly forking caudex becoming columnar from a thatch of marcescent stipules and leaf-stalks, the whole forming tufts or low-convex cushions up to 2 (3) dm. in diameter, the herbage silvery-hirsute with ascending, ± twisted or sinuous hairs up to 1.5-2.8 (3) mm. long, the leaflets equally pubescent on both sides; stipules hyaline, lanceolate or ovate. 7-12 mm. long, united behind the petiole through ¾ or more of their length, fully amplexicaul and in early vernation shortly connate (but the union early ruptured by the expanding shoot), glabrous or nearly so dorsally, thinly hirsute-ciliate, leaves 1.5-3.5 cm. long, the petiole a little widened and flattened at base, the 3 (rarely 1) leaflets narrowly obovate to oblanceolate or elliptic-oblanceolate, acute or sub acute, (3) 5-9 mm. long; peduncles subobsolete, the flowers sessile or nearly so in axillary pairs; bracts hyaline, lanceolate, ovate- or lance-acuminate, or -caudate, sometimes tridentate with short lateral teeth, 3—6 mm. long, pedicels subobsolete; bracteoles similar to the bracts but shorter and narrower, calyx 8.3—10.5 mm. long, densely white-hirsute, the turbinate disc 1—1.2 mm. deep, the cylindric or deeply cylindro-campanulate tube 5.9-6.5 mm. long, 3.1-3.5 mm. in diameter, membranous becoming scarious, fragile, ultimately ruptured dorsally by the expanding ovary the firm, narrowly subulate or almost linear teeth 2.4-4.2 mm. long; petals apparently whitish, pale yellow when faded, all glabrous; banner erect or almost so. narrowly fiddle-shaped, the oblong-oblanceolate claw and blade of about the same length and width, the whole 12.3-17 mm. long, 4.8-5.2 mm. wide, openly notched at apex; wings 11.1-16 mm. long, the claws 4.6-8.5 mm., the narrowly oblong-oblanceolate, obtuse, straight blades 4-8 mm. long, 2.2-2.6 mm. wide; keel 11.1-12.8 mm. long, the claws 7.1-8.2 mm., the subsymmetrically elliptic blades 4.3-4.8 mm. long, 2.2-2.5 mm. wide, incurved through ± 45° to the broadly triangular apex; anthers 0.55-0.8 mm. long; pod erect, sessile, narrowly ellipsoid, 7-10 mm. long, 2.5-3 mm. in diameter, straight or a trifle decurved, somewhat laterally compressed but the sutures not prominent, the sides low-convex, the somewhat fleshy, green, and densely hirsutulous valves becoming leathery, not inflexed; dehiscence downward through both sutures, the valves coiling; seeds not seen.—Collections: 2 (ii), cited below.

Summits of barren, white shale hills and on ridges of gullied shale bluffs, 6500-7100 feet, forming colonies but apparently local, known only from the valley of Henry’s Fork of the Green River near McKinnon, southern Sweetwater County, Wyoming.—Map No. 163.—May (flower), the fruit ripe in late June or early July.

Astragalus proimanthus (precociously flowering), sp. nov., inter A. hyalinum Jones et A. gilviflorum Sheld. quasi intermedia, ilium vexillo brevi platyonychio 12.5-17 mm. tantum longo simulans sed petalis glabris, ovulis 11-14 (nec 8-9) et anthesi vernali (mense Maio in desertis elatis 7000 ped. versus) absimilis, ab hoc floribus minusculis, vexilli forma et legumine anguste ellipsoideo ± 7-10 mm. longo, 2.5-3 mm. diametro ulterius distans.—Densissime caespitosa vel subpulvinata, laxe densissime cano-hirsuta; folia 1.5-3.5 cm., foliola 3 oblanceo- lata vel anguste obovata 3-9 mm. longa; flores bini in stipularum hyalinarum axillis sessiles; calycis 8.3-10.5 mm. longi tubus subcylindricus membranaceus ± 6-6.5 mm. longus dentes firmi 2.4—4.2 mm. longi; petala sicca flava immaculata, omnia glaberrima, caeterius illis A. hyalini simillima, vexillo platyonychio 12.3-17 mm., carina 11-12.8 mm. longis; legumen anguste ellipsoideum, de latere subcompressum, stylo decurvo apiculatum, 1-loculare, valvulis subcarnosis demun coriaceis per suturas ambas dehiscentibus extrorsus tortis; ovula 11-14.— Wyoming: 3 miles north of McKinnon, Sweetwater County, 7100 feet, June 13, 1961, Barneby 13,185.—Holotypus, CAS! isotypi, GH, NY, RM, RSA, US!—First collected June 13, 1946, 6 miles n. of McKinnon, Ripley & Barneby 7913 (RSA).

The precocious orophaca, A. proimanthus, combines some striking characters of each of its close relatives, A. hyalinus and A. gilviflorus. It resembles A. hyalinus in its dwarf habit of growth and in the short flower with its fiddle-shaped, platyonychious banner, but the petals are glabrous and the blooming period is earlier by a month or nearly so. The ovule number lies within the range of variation known in A. gilviflorus, but the narrowly ellipsoid fruit and shorter, differently shaped banner are quite distinct. The plants form comparatively small tufts as in A. gilviflorus, not the very large, high-convex cushions characteristic of A. hyalinus. The relatively loose and spreading pubescence of the leaves lacks the silvery sheen which is one of the most attractive features of the other orophacas. Until well-developed fruit of A. hyalinus is collected, no valid comparison of the pods can be made; however, the tumescent ovary of A. hyalinus is shorter and plumper than that of A. proimanthus at the same stage of growth and contains only 4—5, not 6—7 pairs of ovules. A genuine difference in the ripe pod can be anticipated.

Both collections of A. proimanthus were made on June 13, when the plants were well past anthesis, even though at this date it is still early spring at 7000 feet in the north foothills of the Uintahs. The faded flowers, many of which (in both stations) were eaten away by birds or insects, are of a pale yellow color, papery and fragile. They may have been either white or ochroleucous when fresh.