Astragalus bourgovii 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
"Rocky Mountains on the British Boundary, Bourgeau, in Palliser’s expedition (ex herb. Kew.)."— Holotypus, GH! isotypi, K (from "Montagnes Rocheuses, region alpine, 19 aout, 1858,"), NY, P ("Phaca No. 1, Bourgeau.")!
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Synonyms
Tragacantha bourgovii (A.Gray) Kuntze
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Description
Species Description - Low, slender, usually diffuse, with a taproot and loosely forking, at length suffruticulose caudex, thinly to densely strigulose with fine, straight, appressed hairs up to 0.2-0.6 (0.75) mm. long, the stems sometimes subglabrous, the herbage pale or dark green, more rarely silky-canescent, the leaflets glabrous or medially glabrescent above; stems usually several, weak, decumbent and incurved-ascending, exceptionally erect, (1) 4-15 cm. or (at low elevations) up to 20-25 cm. long, sparingly branched at base or simple; stipules 1-4 mm. long, the lowest, sometimes all, amplexicaul and connate into a papery-scarious, truncate or bidentate sheath, the uppermost ones submembranous, often connate only at base, with lanceolate or lance-acuminate, squarrose blades; leaves 1.5-9.5 cm. long, slender-petioled, or the uppermost ones subsessile, with 11—19 ordinarily elliptic and acute, varying in some or all leaves of some plants to oblong, lanceolate, or broadly oval, in each case either acute, mucronulate, or obtuse leaflets 3—17 (19) mm. long, the midvein rather prominent beneath; peduncles slender, weak, 3—10 (14) cm. long, commonly decumbent or humistrate in fruit; racemes loosely (1) 3—13-flowered, the flowers at first ascending on filiform pedicels, the axis (1) 2—8 cm. long in fruit, bracts membranous or scarious, ovate or ovate-acuminate, 0.7—1.7 mm. long, pedicels densely black-strigulose, at anthesis 1.5—3 (4) mm. long, in fruit either straight and ascending or arched outward, (2) 2.5—4.5 mm. long; bracteoles 0, calyx (3.4) 4.5-6.7 mm. long, densely strigulose with black, more rarely partly white, exceptionally all white hairs, the slightly oblique disc 0.5—1.3 mm. deep, the tube (2.6) 3-4.3 mm. long, the broadly subulate to linear teeth (0.8) 1.2-2.9 mm. long, the whole becoming papery-scarious, marcescent unruptured, petals pink-purple, or pale (drying yellowish) proximally and tipped with purple; banner recurved through ± 50°, ovate- or oval-cuneate, notched, 8-10.5 mm. long, 5-7 mm. wide; wings 7.1-9.3 mm. long, the claws 3.3-4.3 mm., the obliquely obovate- oblanceolate, obtuse or emarginate, slightly incurved blades 4.5-6.2 mm. long, 1.8-2.3 mm. wide; keel 6.7-8.8 mm. long, the claws 3.2-4.4 mm., the lunately triangular blades 3.8-5.1 mm. long, 1.8-2.4 mm. wide, incurved through 90-100 to the bluntly triangular apex; anthers 0.4-0.5 mm. long; pod loosely pendulous but apparently ascending from humistrate peduncles, stipitate, the stipe 1-1.5 (2) mm. long, the body elliptic or oblong-elliptic in profile, straight or a trifle decurved, (7) 9-15 mm. long, 3-4.2 mm. in diameter, narrowly cuneate or acuminate at either end (when relatively short, rounded at base), cuspidate at apex, strongly flattened laterally, bicarinate by the slender, salient sutures, the middle of the valves becoming distended by the seeds, the thin, green, densely black-, black and white-, rarely all white-strigulose valves becoming thinly papery, finely reticulate, not inflexed; ovules 2-6; seeds brown, smooth but dull, 2.2-2.9 mm. long.
Distribution and Ecology - Rocky crests and summits, talus slides, cliff ledges, and open rocky hillsides, most abundant near and above timber line, but descending along streams and locally persisting on shingle banks, gravel bars, and moist grassy banks at middle elevations, commonly but not exclusively on limestone, 4000-8500 feet, well distributed along the main range of the Rocky Mountains from the sources of the Athabaska River, Alberta, south to the Belt, Bridger, and Anaconda Ranges in western Montana, east to the Big Snowy Range in Fergus County, west to the Swan Range in Missoula County, and to the Coeur d’Alene Mountains in Shoshone County, Idaho; reported by Jones (1923, p. 90) from the Sawtooth Mountains, Idaho, and from eastern Montana, both probably, the latter certainly, by error.— Map No. 36.—July to September, flowering in June in the lowland stations.
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Discussion
The Bourgeau milk-vetch has unusually wide altitudinal tolerance and so it occupies a great variety of ecological niches. Normally, or at least most abundantly, it is a montane plant of open slopes within the forest belt and of stony alpine meadows and rock slides above the limit of trees, where it often assumes a dwarfed, subacaulescent, few-flowered aspect remarkable for its very small distant leaflets. Not uncommonly it descends along streams into the intermontane valleys of western Montana, there becoming taller, more erect, more lushly leafy, and floriferous. As Rydberg (1923, p. 186) remarked, the extremes are superficially very different, but they are connected by a series of intermediate forms. The two collections of J. Macoun from Mount Paget, cited above, provide examples of the extremes growing close together. The species is apparently very sensitive to its immediate environment. The whole inflorescence of A. Bourgovii, and especially the fruit, is most often pubescent with black hairs. This dark vesture, of which Rydberg overestimated the systematic importance, combined with purple petals, thin-textured, pendulous pods, and a weakly, straggling habit of growth, is suggestive of some Oroboidei, although the pod is here strictly unilocular and very strongly compressed from each side.
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Objects
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Distribution
Idaho United States of America North America| Montana United States of America North America| Alberta Canada North America| British Columbia Canada North America|