Astragalus leptaleus A.Gray
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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(1): 1-596.
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Family
Fabaceae
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Scientific Name
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Type
"Plains of the Rocky Mountains, near streams ... Nuttall"—Holotypus labeled by Nuttall "Phaca *paucifiora. R. Mts.," BM! isotypi, GH, K!
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Synonyms
Tragacantha leptalea (A.Gray) Kuntze, Phaca leptalea (A.Gray) Rydb.
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Description
Species Description - Weak, delicate, diffuse, with a slender taproot and widely branching subterranean caudex, thinly strigulose with fine, straight, appressed hairs up to 0.2-0.5 mm. long, the stems and herbage bright green, the leaflets glabrous above, the inflorescence commonly nigrescent; stems loosely tufted, in old plants very numerous and entangled, 5-20 (30) cm. long, arising singly or few together from buds on the slender, buried caudex-branches, branched at the first emersed, usually congested nodes, floriferous upward from near or from well below the middle; stipules 2-5 mm. long, thinly herbaceous or submembranous, usually several- nerved, the lowest becoming papery in age, all glabrous dorsally, fully amplexicaul and connate, the lowest into a short bidentate sheath, the upper ones longer, united through half their length or less, sometimes only at very base, with lanceolate free blades; leaves 2.5-10 cm. long, petioled but the uppermost shortly so, with sub- filiform rachis and (9) 15-23 (27) narrowly elliptic or lanceolate and subacute, or (in the lower leaves) often ovate and obtuse, thin-textured leaflets 3-15 mm. long; peduncles filiform, ascending, 2-5.5 cm. long, shorter than the leaf; racemes loosely 1-5 (commonly 2- or 3-)-flowered, the flowers ascending at anthesis, declined thereafter, the axis up to 1 cm. long in fruit; bracts membranous, lanceolate or lance-ovate, 1.3-3.3 mm. long; pedicels at anthesis straight, 1.2-2.1 mm. long, in fruit arched outward, 1.4—2.5 mm. long; bracteoles 0-2, minute when present; calyx 4-5.7 mm. long, densely to quite thinly black- or rarely white-strigulose, the somewhat oblique disc 0.3—1 mm. deep, the campanulate tube 2.7-3.4 mm. long, 1.9-2.4 mm. in diameter, the subulate or lance-subulate teeth 1.1-2.5 mm. long; petals white (sometimes "purplish" fide Jones), the keel-tip maculate with dull bluish-purple; banner recurved through ±45°, ovate-cuneate, notched, 8.5-11.8 mm. long, 4.8-7.2 mm. wide; wings 7.2-9.5 mm. long, the claws 2.7-3.8 mm., the obliquely obovate, oblong-oblanceolate or -elliptic, obtuse or emarginate blades 4.9-6.5 mm. long, 1.8-2.9 mm. wide; keel 6-7.3 mm. long, the claws 2.8-3.9 mm., the obliquely half-obovate blades 3.2-3.9 mm. long, 1.8-2.3 mm. wide, incurved through 85-120° to the bluntly deltoid apex; anthers 0.3-0.5 mm. long; pod pendulous, obscurely stipitate or subsessile, the stipe not over 1.5 mm. long, often reduced to a narrow neck, the body oblong-, lance-, or subclavate-elliptic in dorsiventral view, 8—14 mm. long, 2.5—4 mm. in diameter, slightly decurved, shortly subulate- or cuspidate-beaked, obcompressed and bluntly trigonous, with obtuse lateral angles and low-convex lateral faces, keeled ventrally by the prominent, convexly arched suture, flattened or shallowly and openly sulcate dorsally, the thin, green, sparsely black- or white-strigulose valves becoming stramineous and papery, not inflexed; ovules 6—10; seeds (seldom observed) brown, smooth, lustrous, ± 1.8—2.1 mm. long.
Distribution and Ecology - Forming small scattered colonies or running together into extensively matted growths in moist sedgy meadows, along swales, or on turfy hummocks at the edge of meandering brooks, 2800—8700 feet, locally plentiful but uncommon in the cooler valleys and parks of the Rocky Mountains: western Montana (Flathead Lake and about the headwaters of Red Rock Creek); east-central Idaho (upper Lost River in Custer County); and Colorado (from upper Laramie River south to South Park, Wet Mountain Valley, and the upper Gunnison River); to be expected in western Wyoming.—Map No. 3.—June to August
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Discussion
The park milk-vetch, A. leptaleus, is similar to A. alpinus in its habit of growth and the nature of its slenderly forking subterranean caudex, but is easily recognized by its few tiny, whitish flowers which are often concealed by the tender, prolific foliage, and subsequently by the subsessile or very shortly stipitate, minutely strigulose, unilocular fruit. In the parks of the Colorado Rocky Mountains it is often associated with A. Bodini, but this differs greatly in its determinate superficial root-crown and more numerous flowers of a vivid purple. Being naturally inconspicuous and found only in meadows where showy louseworts and shooting- stars crowd in their thousands through the sedgy turf, A. leptaleus is easily overlooked, although sometimes so plentiful locally as to afford a palatable forage. So far as can be learned from dried specimens, the petals, except for the maculate keel-tip, are always white, but Jones (1923, p. 90) describes the flower as rarely purplish. Jones also traces its range south to Santa Fe, New Mexico, and north into Canada, but at least the latter extension (and also, perhaps, the purple flower) is based on old collections of A. Bodini.
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Objects
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Distribution
Montana United States of America North America| Idaho United States of America North America| Colorado United States of America North America|