Astragalus longissimus
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Title
Astragalus longissimus
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Authors
Rupert C. Barneby
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Scientific Name
Astragalus longissimus (M.E.Jones) Barneby
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Description
30. Astragalus longissimus
Perennial from a woody taproot and knotty root-crown or shortly forked caudex at or just below soil-level, pilosulous with fine, subappressed and narrowly ascending, straight or nearly straight hairs up to 0.6-1 mm. long, the herbage green or subcinereous, the leaflets glabrous, medially glabrescent, or strigulose above; stems few, rather stout, erect or strictly ascending, (1.5) 2-4 dm. long, simple or branched or spurred at 1-3 nodes preceding the first peduncle, floriferous upward from near or shortly above the middle; stipules 1.5-8 mm. long, dimorphic, the small lower ones amplexicaul and connate into a papery, bidentate sheath, becoming fragile and sometimes deciduous in age, the upper ones herbaceous, lanceolate, very shortly or obscurely connate or free; leaves 5.5-15 cm. long, subsessile or the lowest shortly petioled, with 25-39 (45) oblanceolate to narrowly obovate, elliptic, or linear-elliptic, obtuse or mucronulate, mostly flat leaflets (1) 3-14 mm., long; peduncles erect or incurved-ascending, 5-21 cm. long, the first 1-3 usually stout, the later ones slender, equaling or longer than the leaf; racemes loosely or remotely (12) 20-45 (75)-flowered, the flowers early reflexed, the axis elongating, (4) 6-15 (30) cm. long in fruit; bracts linear-lanceolate, 1.5-3 mm. long; pedicels at anthesis 1-2 mm. long, becoming recurved, abruptly deflexed, or straight and declined or divaricate, somewhat thickened, 2-4 mm. long in fruit, persistent; bracteoles 0; calyx 3.2-5 mm. long, densely strigose-pilosulous with white, fuscous, black, or mixed light and dark hairs, the somewhat oblique disc 0.7-1 mm. deep, the tube 2.4-3.5 mm. long, 2.1-3 mm. in diameter, the subulate or triangular- subulate teeth 0.8-1.5 mm. long, the ventral pair sometimes shortest and broadest, the whole becoming papery, marcescent unruptured; petals ochroleucous, drying dull yellow; banner recurved through ± 50° or further in withering, ovate-cuneate, shallowly notched, 5.3—8.3 mm. long, 3.2—5.5 mm. wide; wings (0.1—1 mm. longer) 5.4-8.5 mm. long, the claws 2-3.5 mm., the obovate or narrowly oblong, obtuse or truncate-emarginate blades 3.7—5.5 mm. long, 1.5—2.5 mm. wide, both incurved but the left one more abruptly so from its junction with the claw; keel
6.6 mm. long, the claws 2.1—2.8 mm., the half-obovate or -orbicular blades 2.8-4 mm. long, 1.7-2.5 mm. wide, incurved through 95-105° to the deltoid, often subporrect apex; anthers 0.4—0.5 mm. long; pod pendulous, stipitate, the straight stipe 3—5.5 mm. long, the body narrowly lance-oblong, oblong, or oblong- elliptic in profile, straight or very slightly decurved, 1.4—2.3 cm. long, 4-5 mm. in diameter, cuneate at both ends, obcompressed-triquetrous, carinate ventrally by the prominent thick suture, openly and shallowly sulcate dorsally, the lateral faces low-convex, the lateral angles obtuse, the green, scarcely fleshy valves becoming stramineous, rather stiffly papery, faintly reticulate, inflexed as a partial or sub- complete septum 0.7—1.3 mm. wide; ovules 10—20; seeds pale or purplish-brown, pitted and sometimes prismatically angled, scarcely lustrous, 2-2.5 mm. long.— Collections: 8 (o); representative: E. W. Nelson 6174 (NY, US), 6283 (NY); Jones (from Mound Valley) in 1903 (NY, POM, US).Stony meadows and grassy stream banks in open oak and pine forest, about 7000-7600 feet, apparently not uncommon on the east slope of the Sierra Madre in westcentral Chihuahua.—Map No. 9.—July to September.
Astragalus longissimus (Jones), comb, nov., based on A. Rusbyi var. longissimus (very long, of the stipe) Jones in Proc. Calif. Acad. Sci. II, 5: 662. 1895.—"Type specimen in the National Herbarium. Dr. Palmer, Chihuahua, Mexico, 1885; Pringle same, by streams in the Sierra Madre Mountains, September 23. No. 1219."—Holotypus, US! paratypi (Pringle 1219), ND, NY, US!—Atelophragma longissimum (Jones) Rydb. in Bull. Torr. Club 55: 162. 1928.
Atelophragma Townsendii (Charles Henry Tyler Townsend, b. 1863) Rydb. in Bull. Torr. Club 55: 162. 1928.—"Chihuahua: Sierra Madre, Townsend & Barber 95 ..."—Holotypus, collected in the Sierra Madre 10 miles s.-e. of Colonia Garcia, July 27, 1899, NY (2 sheets)! isotypi ARIZ, K, ND, P, POM, US!
The Townsend milk-vetch, A. longissimus, is variable in size of the flowers and density of the pubescence, the herbage varying from green to cinereous and the leaflets from quite glabrous to thinly or even densely hairy above. A combination of relatively large flowers with abundant vesture corresponds with Rydberg’s concept of Atelophragma Townsendii, but collections from near Colonia Garcia other than the typus show that these characters are not correlated but fluctuate independently one of another. The indumentum of the pod, calyx, and raceme-axis may be monochrome and white, black, or fuscous, but a mixture of pale and darker hairs is most commonly met with. The color of the hairs has, as always, no taxonomic significance.
The close relationship between A. longissimus and A. Rusbyi has been mentioned under the preceding species, from which the present subject differs principally in its longer leaves composed of more numerous pairs of leaflets and in its slightly broader, more densely strigulose pod. It is no longer possible to distinguish the Mexican species by a longer stipe; and even though the ovules are commonly more numerous than in A. Rusbyi, enough overlapping counts are recorded to make the character useless in practice. In general A. longissimus is a coarser plant, with stiffer and more erect stems. In his Revision (1923, p. 186) Jones interpreted A. Rusbyi var. longissimus as equivalent (pro parte) to A. strigulosus Kunth, but it is now scarcely possible to disentangle or attempt a reasonable interpretation of his nebulous concepts in this group of forms or of the figures (op. cit., Pl. 42) designed to illustrate them.