Monographs Details: Astragalus pseudiodanthus 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
Description:Species Description - Diffuse, caulescent perennial, with a long, slender, vertical or oblique taproot and shortly forking or knotty, subterranean caudex, canescently villous nearly throughout with fine, ascending, incumbent, or curly hairs up to 1—1.2 mm. long, the stems mostly thinly so and greenish, the leaflets glabrous above; stems prostrate, radiating, forming loosely woven mats, 2-3 dm. long, buried for a space of 1-3 cm., divaricately branched at most nodes up to the first peduncle and thus tending to form flat, fan-shaped sprays, the branches sometimes largely replaced by peduncles and then floriferous nearly their whole length, flexuous or abruptly zigzag distally; stipules 2-5 mm. long, membranous or early becoming so, the lowest at length papery, fragile, irregularly deciduous, about semiamplexicaul, the upper ones with deltoid-acuminate or triangular, often reflexed blades; leaves 2.5-5 cm. long, shortly petioled or the upper ones subsessile, with (7) 11—19 rather crowded, obovate-cuneate, obtuse or retuse, loosely folded leaflets 3-10 mm. long; peduncles ascending or incurved, 2-3 cm. long; racemes (7) 12—25-flowered, subcompact becoming loose in age, the flowers at full anthesis spreading, declined thereafter, the axis elongating, 2-5 (8) cm. long in fruit; bracts membranous, ovate or ovate-acuminate, 0.6—1.5 mm. long; pedicels early arched out- and downward, at anthesis 0.5—1.1 mm., in fruit slightly thickened, 1.4—1.8 mm. long, persistent; bracteoles 0; calyx 3.8—4.7 mm. long, villosulous with black and white or largely white hairs, the subsymmetric disc 0.7-0.8 mm. deep, the campanulate tube 2.8—3.8 mm. long, 2.1—2.6 mm. in diameter, the triangular-subulate teeth commonly spreading, 1—1.7 mm. long, the whole becoming papery-membranous, ruptured, marcescent; petals reddish-lilac, the banner with a pale, striate lozenge in the fold; banner recurved through ± 45°, ovate- cuneate or somewhat flabelliform, openly notched, 9-10 mm. long, 6.4—7.4 mm. wide; wings nearly as long, 8.9—9.7 mm. long, the claws 3.1—3.7 mm., the lance- oblong, obtuse or subtruncate, nearly straight blades 5.2—6.4 mm. long, 2—2.3 mm. wide; keel nearly as long or a trifle longer than the wings, 8.5-9.3 mm. long, the claws 3.5-3.8 mm., the broadly lunate or half-obovate blades 5.5-6 mm. long, 2.5-3 mm. wide, abruptly incurved through 90-95° to the bluntly deltoid apex; anthers 0.45—0.55 mm. long; pod deflexed, deciduous from a minute boss on the receptacle, very obliquely ellipsoid or lance-ellipsoid, (1.6) 2—3 cm. long, (4.5) 5—8 mm. in diameter, nearly straight in the lower third, thereafter abruptly (and so hamately) incurved through 180°, or more gently but further incurved into a nearly complete ring, cuneate at base, acuminate distally into the laterally compressed, rigidly long-cuspidate beak, otherwise dorsiventrally compressed or sub- triquetrous, the ventral suture commonly depressed at base and salient distally, the dorsal one lying in a wide and open groove extending from base to beak, the somewhat fleshy, green or faintly mottled, at length leathery, stramineous, reticulate or subrugulose valves villosulous with spreading, incumbent, or curly hairs up to 0.6—0.8 mm. long, inflexed at very base or through half the length of the dorsal suture as a very narrow but sometimes almost complete septum 0.3—0.6 mm. wide; dehiscence apical, through the gaping beak; ovules 14—19; seeds olivaceous or purplish-brown, rugulose-punctate, dull, 1.8—2.4 mm. long.

Distribution and Ecology - Dunes and sandy flats, often with Sarcobatus Baileyi and Hilaria Jamesii, about 5550 feet, rare and local, western and northwestern Nye County (Lodi Valley and vicinity of Tonopah), Nevada; also in alluvial soil of former beach, 6800 feet, north shore of Mono Lake, Mono County, California.—Map No. 133.— May and June.

Discussion:The Tonopah milk-vetch, A. pseudiodanthus, is probably a recent derivative of A. iodanthus in which a mutation involving alteration in the type of vesture has coincided with adaptation to a dune or dunelike habitat and withdrawal of the root-crown to the subterranean position so common among psammophytic astragali. I have already noted local minor variants in both varieties of A. iodanthus, in which the pubescence has become incumbent or curly, but the hairs in these forms are shorter, at most up to 0.7 (and not up to 1 or more) mm. long, while the plants are otherwise unlike A. pseudiodanthus, especially in the simpler branching. In size and relative proportion of its parts, the flower of the Tonopah milk-vetch is more nearly like that of the distantly allopatric var. vipereus than that of var. iodanthus, and moreover is substantially smaller than that of the latter as it occurs shortly northward, around the head of the Reese River. In form of the pod A. pseudiodanthus is essentially like A. iodanthus; in the same plant the fruit varies in curvature from an abrupt hook into an almost complete coil.
Distribution:Nevada United States of America North America| California United States of America North America|