Astragalus zacatecanus (Rydb.) Barneby
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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
The type was collected in the state of Zacatecas, in 1897, Rose 2638... Holotypus, NY! isotypi, GH, and with additional data: n"near Monte Escobedo," i.e., in s.-w. Zacatecas, US!
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Description
Species Description - Perennial, strigulose with appressed hairs up to 0.5 mm. long; stems apparently decumbent, nearly 4 dm. long, somewhat branched; stipules 2.5-7 mm. long, all connate, the upper ones more shortly than the lower; leaves 4.5-7.5 cm. long, the upper ones subsessile, with 9-17 oblong to oblanceolate, obtuse or emarginate leaflets 5-20 mm. long, glabrous above; peduncles 8-10 cm. long, surpassing the leaf; racemes 30-55-flowered, early becoming loose, the flowers early declined, the axis 10-18 cm. long in fruit; pedicels at anthesis 1-1.4 mm. long, arched outward, thickened, 2.5-4 mm. long in fruit; bracteoles 0; calyx 6.1-7 mm. long, hirsutulous with mixed dark and pale hairs, the disc about 0.8 mm. deep, the campanulate tube 2.8-3.1 mm. long, 2.5-2.7 mm. in diameter, the lance-subulate teeth 3-4 mm. long; petals apparently ochroleucous, immaculate; banner recurved through 45°, rather narrowly obovate-cuneate, 8.3-9 mm. long, 3.7—4.5 mm. wide; wings 7.6-9 mm. long, the claws 3-4 mm., the narrowly oblong, obtuse, slightly incurved blades 5.6-6 mm. long, about 1.5 mm. wide; keel 6.2-7 mm. long, the claws 2.8-3 mm., the half-obovate blades 4-4.3 mm. long, 2.1 mm. wide, incurved through 90° to the bluntly deltoid, or slightly porrect apex; anthers 0.4 mm. long; pod pendulous, stipitate, the stipe ± 3 mm. long, the body narrowly oblong- ellipsoid, 1.5-2.3 cm. long, 5-6 mm. in diameter, straight, cuneate at both ends, contracted apically into a subulate cusp 1.5-2.5 mm. long, openly sulcate dorsally, the papery valves glabrous, inflexed as an incomplete septum 0.7 mm. wide; ovules 20—24; dehiscence and seeds unknown.
Distribution and Ecology - Habitat unknown, but to be looked for in oak-pine forest at middle elevations, southwestern Zacatecas.—Map No. 8—July to September (?)
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Discussion
The Zacatecas milk-vetch, like the next species, is known only from the typus, and it is impossible to foresee in what measure future botanical exploration of central Mexico will affect their status. Both species are evidently related to A. strigulosus but differ in their elongated fruits of slender outline which enclose ten to twelve pairs of ovules. The present species is chiefly remarkable for its very numerously flowered, at length elongate racemes, and differs further from A. jaliscensis in its comparatively few leaflets and slightly smaller flowers.
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Distribution
Zacatecas Mexico North America|