Astragalus nudisiliquus A.Nelson
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Authors
Rupert C. Barneby
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Authority
Barneby, Rupert C. 1964. Atlas of North American Astragalus. Mem. New York Bot. Gard. 13(2): 597-1188.
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Family
Fabaceae
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Scientific Name
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Type
"Secured by Nelson and Macbride on the steep cobblestone bluffs of the Snake River, at King Hill, Idaho, July 15, 1911, no. 1088."—Holotypus, RM! isotypus, GH!
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Synonyms
Xylophacos nudisiliquus (A.Nelson) Rydb.
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Description
Species Description - Caulescent, diffuse or prostrate, with a taproot and loosely forking, rather soft caudex, densely villous-tomentose throughout with fine, shorter, curly together with longer, straighter, ascending and spreading hairs up to (0.8) 1-1.5 mm. long, the stems white-felted, the herbage silky-canescent in youth, becoming white- cottony late in the season, the leaflets usually equally pubescent on both sides, rarely more thinly so and greenish above; stems several or numerous, radiating, (2) 5-25 (30) cm. long, commonly branched below the middle, together forming loosely woven mats, the longer internodes up to 1—3.5 cm. long; stipules thinly herbaceous becoming membranous, ovate or lanceolate, acute or acuminate, (1.5) 3-7 mm. long, semi- or almost fully amplexicaul-decurrent; leaves 3-11 cm. long, with flaccid, wholly deciduous petiole and (7) 11-17 broadly obovate, obovate- cuneate, or broadly oblanceolate, mostly obtuse, less often subacute or subretuse, flat or loosely folded leaflets 4-17 mm. long; peduncles 1-7 cm. long, incurved- ascending at anthesis, prostrate in fruit; racemes shortly and loosely (2) 4-8- flowered, the axis little elongating, 0.5-2.5 cm. long in fruit; bracts membranous with green midrib, linear-lanceolate, lance-acuminate, or rarely ovate, (1.5) 3-6 mm. long; pedicels ascending or somewhat arcuate in age at anthesis slender, 1 4-2 8 mm., in fruit thickened, 2-3.4 mm. long; bracteoles 0-2, sometimes conspicuous and up to 2 mm. long; calyx (14.6) 15-18 8 mm. long thinly villosulous with white or white and a few black hairs, the subsymmetric disc 1.6-2.7 mm. deep, the membranous, purplish, cylindric tube (11.3) 12-13.8 mm. long, (5 5) mm. in diameter, the subulate or subulate-setaceous teeth (2) 3 5 mm. long; petals pink-purple, the banner with a pale, striate eye, the color fugitive when dried; banner recurved through ±40°, spatulate-oblanceolate, 20.5-25 5 mm. long the rhombic-ovate, notched blade 9-12 mm. wide, wings 18.3 23.3 mm. long, the claws 11.4-14 mm., the lanceolate, obtuse blades (8.1) 9-11 mm. long, 2.5-3 mm. wide, gently incurved in the distal ?; keel 17.4-21.3 mm. long, the claws 11.2-14.3 mm., the lunately half-obovate blades 6.6-8 mm. long, 2.7 3.3 mm. wide; anthers 0.5-0.7 mm. long; pod ascending (humistrate), obliquely ovoid or oblong-ellipsoid, (1.5) 2-3.5 (4.5) cm. long, (8) 9—13 mm. in diameter, at base rounded, broadly cuneate, or abruptly contracted into a short, obconic neck, strongly obcompressed, openly depressed-sulcate ventrally and flattened dorsally through the proximal ? or more, thence passing upward into a strongly incurved or even backwardly hooked, triangular- or lance-acuminate, laterally compressed beak, the green, fleshy valves becoming stiffly leathery, brown or stramineous and (0.5) 0.6-1 mm. thick when ripe, faintly rugulose and also wrinkled lengthwise along either side of the thick ventral suture, not inflexed, but the dorsal suture sometimes thickened and slightly elevated within, the whole relatively thinly villous-hirsute with lustrous, spreading hairs up to 1.6—2.5 (3) mm. long, the vesture not concealing the surface of the valves, sometimes deciduous in extreme age; dehiscence apical, after falling; ovules 30-41; seeds brown or nearly black, sparsely pitted, dull, 2.3—2.8 mm. long.
Distribution and Ecology - Summits and gullied slopes of river bluffs and terraces, in sandy clay or cobblestone alluvia, 2100—3300 feet, locally plentiful along the Snake and the lower Malheur and Bruneau Rivers about the west end of the Snake River Plains, from northern Malheur County, Oregon, and Payette County, Idaho, upstream to Elmore County.—Map No. 88.—Late April to early July.
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Discussion
The cobblestone milk-vetch—its epithet nudisiliquus is ordinarily inappropriate and misleading—is quite similar to A. utahensis in habit of growth, in vesture, and in detail of the only slightly less handsome and amply proportioned flower. It is distinguished principally by the broader, often longer, at first fleshy and ultimately subligneous pod which is, by comparison with the majority of the Eriocarpi, only thinly hirsute, the hairs being spaced so as to reveal the surface of the valves. The vesture is deciduous only in extreme age, as shown in the type- collection, where the pod had already (by mid-July) fallen and split open to release the seeds. Two other purple-flowered Eriocarpi are found in the same range as A. nudisiliquus, one (A. Purshii var. glareosus) at greater elevations and in less specialized environment, the other (A. Purshii var. ophiogenes) in almost identical habitats. The var. glareosus has flowers of about the same size but fewer, and shorter, ordinarily tufted stems; the var. ophiogenes has flowers hardly half as large.
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Objects
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Distribution
Oregon United States of America North America| Idaho United States of America North America|