Astragalus porrectus S.Watson
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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
“Trinity Mountains, Nevada; 5000 feet altitude; May ([Watson] 284)."— Holotypus, collected in 1868, US! isotypus, GH!
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Synonyms
Tragacantha porrecta (S.Watson) Kuntze, Homalobus porrectus (S.Watson) Rydb.
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Description
Species Description - Stiff, sparsely leafy, with a woody taproot and loosely forking, at length indurated caudex, thinly strigulose with straight, somewhat flattened, truly appressed hairs up to 0.3-0.5 mm. long, the stems glabrous or nearly so below the middle, the herbage green, the leaflets glabrous on both sides, sparsely ciliate; stems several, erect and ascending in bushy clumps, 2.5-4 dm. long, leafless at base, branched or spurred at 1-4 nodes preceding the first peduncle, flexuous or zigzag distally; stipules scarious or early becoming so, 2-9 mm. long, the lowest of the main stems and of the more slender branches connate into an amplexicaul sheath (sometimes ruptured in age), the median and upper ones deltoid or deltoid-acuminate, semiamplexicaul, their margins beset with a few minute processes; leaves shortly petioled or the upper ones subsessile, 3.5-11 cm. long, with 9-13 rather distant, broadly obovate-cuneate or -flabellate, very obtuse to shallowly retuse, flat, thick-textured leaflets 7-15 (18) mm. long, the midrib prominent beneath and giving rise to 1-3 pairs of semi-immersed lateral veins; peduncles stiffly erect, 3.5-15 cm. long, the lower ones far longer than the leaf, the early inflorescences often overtopping the more shortly pedunculate later ones; racemes very loosely or remotely (7) 12-33-flowered, the axis 4—20 (28) cm. long in fruit; bracts membranous, linear-lanceolate or subulate, 1-3.4 mm. long; pedicels ascending, straight or nearly so, at anthesis 0.5-2 mm., in fruit little thickened, (0.9) 1.2-2 mm. long; bracteoles 0; calyx 4.7-5.5 mm. long, black-strigulose, the subsymmetric disc 0.7-0.8 mm. deep, the tube 3-3.5 mm. long, 2.2-3 mm. in diameter, the narrowly subulate teeth 1.7-2 mm. long, the ventral pair often shortest, the orifice oblique, the whole becoming papery, marcescent unruptured; petals white, drying ochroleucous; banner 8—11 mm. long, the cuneate claw expanded into an ovate or sub- orbicular, emarginate blade 5-7 mm. wide; wings 7.8-9 mm. long, the claws 3-3.5 mm., the broadly oblanceolate, obtuse or obscurely emarginate, nearly straight or gently incurved blades 5.3—6.9 mm. long, 2—2.6 mm. wide; keel 6.8—7.7 mm. long, the claws 3.2-3.5 mm., the half-obovate blades 4-4.7 mm. long, 2.2-2.5 mm. wide, incurved through 95° into the bluntly deltoid apex; anthers 0.4—0.6 mm. long; pod incurved-ascending, stipitate, the straight or slightly incurved stipe spreading from the raceme at a wide angle, (2.5) 3-5 mm. long, the body lunately oblong-ellipsoid, 8-15 mm. long, 3—5 mm. in diameter, incurved through ± ¼ circle, cuneate at base, abruptly cuspidate at apex, laterally compressed, bicarinate by the salient, riblike sutures, the lateral faces concave along the ventral suture and convex along the dorsal one, the moderately fleshy, glabrous, green or sometimes purple-tinged or -mottled valves becoming leathery, stramineous sometimes suffused with purplish-brown, transversly reticulate, not inflexed; seeds brown, smooth, 2.5-3 mm. long.
Distribution and Ecology - Hot gravelly washes and outwash fans in the foothills of desert mountains, in volcanic sand or rock-debris, 4300—5000 feet, rare and local, known only from the lower Humboldt and Truckee Valleys in Churchill, Pershing and southern Washoe Counties, Nevada.—Map. No. 70.—May and June, the fruit long persisting.
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Discussion
A rather tall, stiffly branching but nonetheless airily graceful plant, A. porrectus is readily recognized by its scarious sheathing lower stipules, by its few, almost glabrous leaflets of broad outline and leathery texture loosely disposed along a stiff, tapering rachis, and by its open racemes of small, white flowers which give rise to stipitate, incurved, laterally compressed pods carinate along both edges by salient sutures. The species has been collected seldom, and in the two stations known to me only a few plants were found. It is restricted in range to the bed of Lake Lahontan, the body of water that covered a large part of westcentral Nevada at intervals during the Pleistocene. It seems hardly credible that A. porrectus, so greatly isolated taxonomically, could have evolved in situ in the relatively short period of time during which its habitat has been available to continuous colonization by higher plants. Possibly it is a relic of a formerly more widely dispersed flora which, having survived (by adaptive mutation) the vicissitudes of climatic change, has found refuge in the non-competitive, however austere environment of a desert sink. It might appropriately be called the Lahontan milk-vetch.
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Objects
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Distribution
Nevada United States of America North America|