Astragalus shortianus Nutt.
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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
"Rocky Mountains, towards the plains of the Oregon...Nuttall"— Holotypus, labeled "Astragalus *Shortianus. R. Mts. Nuttall" BM!
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Synonyms
Tragacantha shortiana (Nutt.) Kuntze, Xylophacos shortianus (Nutt.) Rydb., Astragalus shortianus var. typicus Barneby
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Description
Species Description - Low, tufted, often quite amply leafy, essentially acaulescent, with knotty root-crown or shortly forking caudex, densely silky-strigulose or -strigose with fine, appressed or some narrowly ascending, straight or nearly straight hairs up to 0.75-1.25 mm. long, the calyx villous, the herbage silvery or rarely greenish, the leaflets commonly equally pubescent on both sides, sometimes more thinly so above; stems nearly always reduced to sessile crowns, exceptionally up to 2.5 cm. long, but the internodes all concealed by stipules; stipules thinly herbaceous becoming papery and brownish, several-nerved, lanceolate, lance-oblong, or -acuminate, the lowest sometimes ovate, (3) 5-12 mm. long, decurrent-amplexicaul around ½ to the whole stem’s circumference, free; leaves (4) 6-21 cm. long, with rather stiff, grooved petiole and 7—17 (19) obovate, rhombic-obovate, elliptic-ovate, rarely flabellate, obtuse, or rarely subacute, flat or loosely folded leaflets 5-20 (25) mm. long; peduncles usually stout, 2-15 cm. long, shorter (except at earliest anthesis) than the leaves, arcuate-procumbent or prostrate in fruit; racemes shortly but loosely (5) 7—16-flowered, the axis little elongating, 1-4 (6) cm. long in fruit; bracts membranous with green midrib, linear-lanceolate or -caudate, 4-10 mm. long; pedicels at anthesis slender, 1.6-2.8 mm. long, in fruit ascending or arched outward, thickened, (2) 3—4 mm. long; bracteoles usually 0, rarely 2, exceptionally conspicuous; calyx (9.4) 11-14.7 long, villous with loosely ascending or spreading hairs over 1 mm. long, the oblique disc 1.4-2 mm. deep, the membranous, usually purplish, cylindric or deeply campanulate tube (6.5) 7.6-9.8 mm. long, 3.6-4.8 mm. in diameter, the lance-subulate teeth 2.9-5.6 mm. long, the ventral pair commonly broader and often a trifle longer than the rest; petals pink-purple with pale claws and a pale lozenge in the fold of the banner; banner gently recurved through ± 40°, broadly spatulate to ovate-cuneate, (16) 19—22 mm. long, 7.5—11 mm. wide; wings nearly as long, (15) 17.2-20.1 mm. long, the claws (7.7) 8.6-10.3 mm., the lance-oblong, obtuse or truncate-emarginate blades (8.2) 9-11.6 mm. long, 2.8-3.9 mm. wide, slightly incurved in the distal half; keel (13) 15.5—17.2 mm. long, the claws (8) 9.3-10.3 mm., the half-obovate blades 6—7.7 mm. long, 3.2—4.2 mm. wide, rather abruptly incurved through 85-95° to the bluntly deltoid apex; anthers 0.55-0.85 (0.9) mm. long; pod ascending (humistrate) obliquely ovoid or ellipsoid, (2) 2.5-4.5 cm. long, (8) 9-18 mm. in diameter, rounded or sometimes obtusely cuneate at base, obcompressed and nearly straight in the lower ?, thence passing upward into a strongly incurved, deltoid- or lance-acuminate, laterally compressed, rigid beak, shallowly depressed-sulcate along both sutures or merely flattened dorsally, the sutures both (but the ventral especially) prominent and cordlike, the green, fleshy, rather densely strigulose valves becoming woody or very stiffly leathery, brown, stramineous, or ultimately blackish, rugulose-reticulate, commonly not inflexed, but sometimes obscurely so, the septum forming a tubular cavity behind the ventral suture and extending inward ± the depth of the valve-wall, this 0.6—1.2 mm. thick when ripe; dehiscence apical, through the beak, tardy; ovules 33-54 (66); seeds brown or purplish-brown, pitted or wrinkled, (2) 2.6-3 mm. long.
Distribution and Ecology - Prairies, dry hilltops, open stony ridges, or cobblestone bluffs, commonly on decomposed granite, occasionally on sandstone, coarse alluvia of mixed origins, and perhaps other bedrock, 5200—9000 feet, frequent and locally plentiful on the east slope and piedmont of the Rocky Mountains drained by the North Platte, South Platte, and Arkansas Rivers in southeastern Wyoming and Colorado, extending more rarely across the Divide in Colorado to the upper Grand River, south to the head of the Canadian River and the upper Rio Grande in northern New Mexico, and northwest to the Wind and Big Horn Rivers in westcentral Wyoming; an old report from the Black Hills (Geyer) requires confirmation; records from western Colorado (other than in Eagle and Grand Counties) were based on collections of A. iodopetalus.—Map No. 82.—May to July.
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Discussion
On the Laramie Plains and southward along the east slope of the Front Range as far as South Park, Short’s milk-vetch is one of the common ornaments of spring. The large, rosy- purple flowers which are borne on short, subradical stalks expand rapidly with the approach of warm weather and fade before the loosely tufted foliage reaches its full development. The young leaves are silvery-silky and may remain so throughout the season, but often, especially when of ample size, turn greenish in age. Except for the villous-hirsute A. Parryi, the present species is the only member of its section with basifixed pubescence in its area of dispersal and is seldom misidentified. It has been confused only with A. iodopetalus, probably because the calyx of both is loosely pubescent and long-toothed, but A. Shortianus is easily distinguished by its fewer leaflets and ordinarily much larger or broader, thinly pubescent and not glabrous pod. The differential characters of the more nearly related A. cyaneus are mentioned below.
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Objects
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Distribution
Wyoming United States of America North America| Colorado United States of America North America| New Mexico United States of America North America|