Astragalus thurberi 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(2): 597-1188.
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Family
Fabaceae
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Scientific Name
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Type
"Near Fronteras, &c., Sonora; in dry places; June, 1851. No. 327."—Holotypus (Thurber 372), GH! istoypi, K, NY (2 sheets)!
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Synonyms
Tragacantha thurberi (A.Gray) Kuntze, Phaca thurberi (A.Gray) Kearney
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Description
Species Description - Low and diffuse, rather coarse, perennial but of short duration, sometimes flowering and fruiting the first year, with a taproot and at length indurated root- crown, strigulose nearly throughout with straight, appressed or subappressed hairs up to 0.35-0.55 mm. long, the herbage green, the growing tips sometimes cinereous. the leaflets glabrous above; stems several or numerous, decumbent and ascending in low bushy clumps, (0.7) 1.5-4 dm. long (in seedlings sometimes solitary, erect, already fruiting when only 3—1- cm. tall), striate, spurred or branched at 1-3 (5) nodes preceding the first peduncle, flexuous or zigzag distally; stipules (2) 3-8 mm. long, the lowest early becoming papery, deltoid-ovate, the upper ones longer and narrower, submembranous, triangular or triangular-acuminate, decurrent around half to nearly the whole stem’s circumference, the margins commonly beset with a few minute processes; leaves (2) 4-10 (11.5) cm. long, all petioled but the uppermost shortly so, with (9) 13-21 oblong-elliptic, oblanceolate, or linear-elliptic, obtuse, truncate and mucronulate, or shallowly retuse, flat or loosely folded leaflets 5-15 (18) mm. long; peduncles commonly rather stout, erect or incurved-ascending, 3-8.5 mm. long, a little shorter or longer than the leaf; racemes (7) 10-25 (32)-flowered, rather dense in early anthesis, becoming loose in age, the flowers ultimately spreading, the axis (2) 3-7 (11) cm. long in fruit; bracts lanceolate, broadly membranous-margined, 1-2.4 mm. long; pedicels at anthesis ascending, straight, 0.5-1 mm. long, in fruit arched outward, a trifle thickened, 1-1.8 mm. long, persistent; calyx 3.3-5 mm. long, strigulose with white and sometimes a few black hairs, the slightly oblique, turbinate disc 0.6-1 mm. deep, the tube 2.2-2.9 mm. long, 1.7-2.2 (2.5) mm. in diameter, the erect, subulate or lance-subulate teeth (1) 1.3-2.3 mm. long, the ventral pair often longest, the whole becoming papery, ruptured, marcescent; petals reddish-lilac or -purple; banner at full anthesis recurved through ± 50° (sometimes further in withering), 5.7-7.1 mm. long, the short-cuneate claw abruptly expanded into a broadly ovate or suborbicular, shallowly notched blade 4.2-5.7 mm. wide; wings 5.1-6.7 mm. long, the claws 1.8-2.5 mm., the oblong- obovate, obtuse but often erose-undulate, slightly incurved blades 3.6-4.8 mm. long, 1.6-2.3 mm. wide; keel 4.7-5.6 mm. long, the claws 2.2-2.7 mm., the halfcircular or -obovate blades 2.6-3.4 mm. long, 1.7-2 mm. wide, abruptly incurved through 100-105° to the obtusely deltoid, sometimes obscurely porrect apex; anthers 0.35-0.55 mm. long; pods crowded and subcontiguous in narrowly oblong or cylindrical heads, spreading or a little declined, sessile on and disjointing from the conic receptacle, the body very broadly and plumply ovoid- or obovoid-ellip- soid, obovoid, or subglobose, bladdery-inflated, 6-13 mm. long, 6-10 mm. in diameter, rounded at base, contracted distally into a very short or subobsolete, triangular beak, obscurely or not at all sulcate along the subequally convex sutures, the thin, green or minutely purple-dotted, sparsely strigulose valves becoming papery, stramineous, delicately cross-reticulate, not inflexed, the funicular flange 0.3-0.6 mm. wide; dehiscence apparently apical, tardy, after falling, ovules 8-11; seeds golden- or ocher-brown, smooth or sparsely pitted, dull, 1.7-2.4 mm. long.
Distribution and Ecology - Plains, valleys, open hillsides, in dry sandy or gravelly soils, sometimes on semistabilized dunes, with Larrea, oak brush and juniper, or in mesquite-grassland, without apparent rock preference, 3000-6000 feet, rather common and locally abundant in favorable years, southeastern Arizona, southwestern New Mexico, and northeastern Sonora, presumably in adjoining Chihuahua.—Map No. 120.—March to May.
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Discussion
Flowering specimens of the Thurber milk-vetch suggest a form of A. Wootoni with twice as many flowers to the raceme; growth-habit and details of foliage, vesture, and parts of the flower up to the reduced number of ovules in A. Thurberi are closely similar in the two species. Fortunately both of them flower and bear fruits early in the season, when the Thurber milk-vetch is readily told from the related and partly sympatric A. Wootoni and A. allochrous by its comparatively tiny, plumply obovoid or subglobose pod. The species is locally abundant in parts of southeastern Arizona and adjoining New Mexico, where it has the reputation of being highly poisonous, especially to horses.
The Thurber milk-vetch was identified by Jones (1933, p. 45) with a South American member of sect. Inflati, A. coquimbensis (H. & A.) Reiche, a species of coastal desert in northern Peru which is similar in gross aspect but differs in many details. The root of A. coquimbensis appears to be truly annual and always short-lived, the raceme is only about 7-10 (not on the average 10-25)-flowered and the flowers themselves are slightly but significantly larger. Furthermore the pods are fewer, less crowded, and larger (about 12-25 X 8-15, not 6-13 X 6-10 mm.) and the ovules more numerous (12-17, not 8-11). The pod of A. coquimbensis apparently falls together with the pedicel as in the other South American Inflati and not, as in A. Thurberi, by disjointing from the receptacle. The relationship is evident but not really close.
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Objects
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Distribution
Arizona United States of America North America| New Mexico United States of America North America| Sonora Mexico North America| Chihuahua Mexico North America|