Astragalus scalaris 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
"By streams in the Sierra Madre, Chihuahua (no. 1220), September 1887."—Holotypus, collected September 23, 1887, by C. G. Pringle, GH! isotypi, K, ND, NY, PH, US!
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Synonyms
Phaca scalaris (S.Watson) Rydb., Astragalus scalaris var. quercetinus M.E.Jones
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Description
Species Description - Erect, slender, graceful, proportionately tall, finely strigulose with straight, appressed hairs up to 0.2-0.4 mm. long, the green, striate stems becoming stramineous, the herbage green, the leaflets glabrous above; stems often solitary, rarely more than 3, stiffly and strictly erect from the superficial crown of a taproot, paniculately branched upward either from near the base or from near the middle, the branches either simple or again branched, all floriferous distally, the whole (2) 3—9 dm. tall; stipules submembranous, triangular or triangular-acuminate, 1.5-5 mm. long, decurrent around one-fourth to nearly half the stem’s circumference; leaves (1.5) 3.5—13 cm. long, the lowest shortly petioled, the rest subsessile, with slender, tapering rachis and (11) 17-27 (31) slender-petiolulate, rather distant, linear-oblong, narrowly lance-elliptic, or more rarely oblong-ovate, thin-textured, flat, faintly penninerved leaflets (1.5) 3-13 mm. long, all retuse or some narrow ones obtuse and apiculate; peduncles erect or incurved-ascending, mostly very slender, 3-10 cm. long, either shorter or longer than the leaf; racemes very loosely or remotely 15—50-flowered (or the subterminal, depauperate ones only 5-10-flowered), the flowers spreading, the axis elongating, (2) 4-20 cm. long in fruit; bracts membranous, ovate-acuminate, narrowly triangular, or lanceolate, 0.7—2 mm. long; pedicels ascending, straight or arched outward in age, at anthesis slender, 0.7—1.5 mm. long, in fruit thickened, 0.8—2 mm. long; bracteoles 0, calyx 2.2—2.9 mm. strigulose with black hairs, the subsymmetric disc 0.40.6 mm. deep, the shallowly campanulate or hemispherical tube 1.6—2 mm. long, 1.7-2 mm. in diameter, the triangular or deltoid teeth 0.5-1 mm. long, the ventral pair shorter and broader than the rest, the orifice oblique, the whole becoming papery, marcescent unruptured; petals pale pinkish-purple, or whitish distally purple-tinged, drying pallid or ochroleucous; banner recurved through ± 45°, broadly ovate-cuneate, shallowly notched, 5.2-6.4 mm. long, 3.6-4.8 mm. wide; wings 5-5.5 mm. long, the claws 1.6-1.9 mm., the oblong or oblong-oblanceolate, obtuse or truncate-emarginate, nearly straight blades 3.6-4.2 mm. long, 1.4-2.3 mm. wide; keel 3.9-4.7 mm. long, the claws 1.5-1.9 mm., the obliquely triangular-obovate blades 2.6-3 mm. long, 1.7-2.1 mm. wide, incurved through 85-95° to the blunt, deltoid apex; anthers 0.3-0.4 mm. long; pod horizontally spreading or declined, persistent on the receptacle, shortly stipitate, the stipe (0.4) 0.5-1.3 mm. long, concealed by the calyx, the body obliquely obovoid or half-obovoid, (4) 5-8 mm. long, 2.5-3.5 mm. in diameter, slightly inflated, broadly cuneate or rounded at base, abruptly contracted distally into a very short, broadly deltoid, slightly incurved, laterally flattened, minutely cuspidate beak, otherwise obtusely triquetrous, carinate ventrally by the straight or low-convex suture, openly and shallowly sulcate dorsally up to the base of the beak, the thin, green, glabrous valves becoming papery, stramineous, delicately reticulate, not inflexed or inflexed as a rudimentary septum up to 0.15 mm. wide; seeds brown, smooth, lustrous, 2-2.5 mm. long.
Distribution and Ecology - Streamsides and moist places in ravines, canyons, or open pine and oak forest, 6000-8000 (acc. Jones up to 9500) feet, known only from the Sierra Madre Occidental in Chihuahua.—Map No. 12.—August to October.
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Discussion
The Chihuahua milk-vetch, A. scalaris, is instantly recognized by its slender, strictly erect, airily branching stems which are often solitary and rarely more than three in number, by its rather numerous small leaflets, and by the remotely many-flowered racemes of tiny, purplish flowers followed by small, spreading, substipitate, turgid pods of obliquely obovoid form and devoid of all but a rudiment of septum. The few ovules and large seeds are other noteworthy features of this delicately delightful species. The plants vary a great deal in stature, some of those in the type-collection of var. quercetinus being nearly a meter tall, but there seems to be no good reason to recognize a variety which does not differ significantly in other respects. There is some doubt as to the duration of the root under average circumstances. Watson described A. scalaris as biennial, and some very slender individual plants appear to be flowering in their first season. Others, however, bear remnants of growth from preceding years, and the species must be at least potentially perennial. The meaning of the epithet scalaris, to which Watson gave no clue, remains an enigma.
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Objects
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Distribution
Chihuahua Mexico North America|