Astragalus sophoroides M.E.Jones
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Authors
Howard S. Irwin, 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
"Collected at Willow Springs and on the Moencoppa, northern Arizona, June 10, 1890."—Holotypus, from Willow Springs, POM (4 sheets)! paratypi, from Moencoppa, June 11, 1890, POM (2 sheets), MO, US!
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Synonyms
Cnemidophacos sophoroides (M.E.Jones) Rydb.
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Description
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Species Description - Low, loosely tufted, shortly caulescent, with a slender but in older plants toughly woody taproot and shortly forking caudex, densely strigose-strigulose throughout with straight, appressed and subappresed, somewhat flattened hairs up to 0.7-1.1 mm. long, the stems canescent, the leaflets silvery or greenish- cinereous, pubescent on both faces but sometimes more thinly so above than beneath; stems several, slender, 2.5-20 cm. long, erect or the outer ones decumbent with incurved-ascending tips, composed of ± 6-12 internodes up to 0.3-3.5 cm. long, simple or spurred at the lower axils, commonly zigzag distally; stipules scarious or early becoming so, (1) 2-5 (7) mm. long, all amplexicaul and all or at least the lowest connate through half or more than half their length, with triangular, deltoid, or triangular-acuminate, erect or spreading blades; leaves 3-8 (12) cm. long, all petioled, with 7-13 narrowly oblong or linear-elliptic, subacute or obtuse, flat or loosely folded, rather distant leaflets 3-12 (21) mm. long; peduncles (0.7) 1-3 (4) cm. long, narrowly ascending, much shorter than the leaf; racemes 7-17-flowered, rather dense, the ascending flowers and fruits often subcontiguous, the axis little elongating, (0.7) 1-4 cm. long in fruit; bracts thinly herbaceous becoming scarious, ovate or lanceolate, 2-5 mm. long; pedicels narrowly ascending, straight, at anthesis 0.5-0.7 mm., in fruit somewhat turbinately thickened, 0.7-1 mm. long; bracteoles 0; calyx at anthesis 5-6.3 mm. long, densely (in age sometimes loosely) white-strigulose, the subsymmetric disc 0.6-0.8 mm. deep, the campanulate or turbinate-campanulate tube 3-3.6 mm. long, 2-2.6 mm. in diameter, the lance-subulate teeth 2-3 mm. long, the whole becoming scarious and a trifle accrescent, either ruptured or not, finally investing the pod; petals reddish-lilac, the banner with a pallid, striate eye, fading dull straw-color, withering-persistent; banner recurved through 45°, ovate-cuneate, 8.5-10 mm. long, 5.2-6.7 mm. wide; wings 7.6-8.8 mm. long, the claws 3-3.3 mm., the elliptic or ovate-elliptic, obtuse or obscurely emarginate, slightly incurved blades 5.1-6.3 mm. long, 2-2.8 mm. wide, the inner margin of the left one incurved over the keel; keel 5.7-6.8 mm. long, the claws 2.9-3.5 mm., the half-obovate blades 3-3.8 mm. long, 1.8-2.4 mm. wide, abruptly incurved through 100-105° to the bluntly deltoid apex; anthers 0.4-0.5 mm. long; pod erect or narrowly ascending, sessile on a minute boss, oblong-ellipsoid, 6.5—8 mm. long, 3—4 mm. in diameter, obtuse at base, contracted distally into a very short, laterally compressed, deltoid- triangular beak, either straight or a trifle incurved, strongly obcompressed below the beak, flattened dorsally, carinate ventrally by the prominent but depressed suture, the thinly fleshy, canescently strigulose valves becoming stiffly papery, stramineous, faintly cross-reticulate, not inflexed; dehiscence apical and downward through the ventral suture; ovules 4—6; seeds brown, smooth and lustrous, 2.3-3.1 mm. long.
Distribution and Ecology - Sandy flats and knolls, on ledges and in sandy pockets of dry cliffs, in desert washes, rarely on sand bars of running streams, commonly on red sandstone, forming colonies but very local, known only from the lower Little Colorado River and Moenkopi Wash, at 4200—4900 feet, in eastern Coconino County, Arizona.— Map No. 43.—May to June.
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Discussion
The Painted Desert milk-vetch, A. sophoroides, is closely related to A. flavus var. candicans, of which it may be a specialized derivative of recent creation. Flowers and fruits of the two are closely similar in form and arrangement, although the slightly accrescent calyx, marcescent petals, and few ovules of A. sophoroides are peculiar. It is possible that the last two features have been derived by introgression from the sympatric A. moencoppensis, but nothing else about the species suggests such a cross. The short peduncles give the mature plant a characteristic squat and leafy appearance which is instantly recognized. Despite the lively reddish-lilac coloring of the newly opened flowers, A. sophoroides is a modest and inconspicuous astragalus. It is apparently restricted in range to an area of some ten to fifteen miles in diameter around the northern edge of the Painted Desert, extending from the neighborhood of Cameron north to Willow Spring and Tuba City, but is common locally in the region. At Cameron it has been found on sand bars of the Little Colorado, and it is fairly certain to be traced downstream eventually in the direction of Grand Canyon.
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Objects
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Distribution
Arizona United States of America North America|