Astragalus whitneyi 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(1): 1-596.
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Family
Fabaceae
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Scientific Name
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Type
"On the same mountain with the preceding species," i.e., "Dry rocky mountain near Sonora Pass ... in loose soil, near the summit, alt. 10,000 feet."—Holotypus, collected by G. H. Brewer in 1863, wrongly dated "1866," GH! isotypi, K, P, US!
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Description
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Species Description - Variable in stature, usually low, slender, diffuse and ascending, less often moderately tall and stout, with a thick, woody taproot and nearly always shallowly buried root-crown or caudex, densely to sparsely pubescent with appressed, in- curved-ascending, or rarely spreading hairs up to (0.3) 0.35-0.8 mm. long, the herbage greenish, cinereous, or silvery-canescent, the leaflets glabrous, medially glabrescent, or densely hairy above; stems several or numerous, 2-30 (40) cm. long, leafless and purplish at base, commonly branched or spurred at 1-4 nodes preceding the first peduncle, sometimes simple, flexuous or zigzag distally; stipules 1-5 mm. long, all or at least those at the lowest nodes papery, pallid, purplish or brownish, connate into a loose, cuplike, or shallowly bidentate sheath, the median ones often united only at base or through half their length, the uppermost sometimes only semiamplexicaul, with subherbaceous, triangular, often reflexed blades; leaves 1.5-10 cm. long, shortly petioled, with (5) 9-21 oblong-oblanceolate, elliptic, or narrowly obovate, obtuse, or sometimes linear-elliptic and subacute, flat, folded, or involute leaflets 2—21 mm. long; peduncles incurved-ascending or erect, 1-9.5 (12) cm. long; racemes loosely (3) 4-16-flowered, the flowers spreading and ultimately declined, the axis not greatly elongating, 0.5—7 cm. long in fruit; bracts papery or early becoming so, ovate-triangular or lanceolate, 1—3 mm. long; pedicels at anthesis slender, ascending, (0.5) 0.8—1.3 mm. long, in fruit a trifle thickened, arched outward, 1—2.5 mm. long; bracteoles usually 0, rarely 1—2 minute scales; calyx 4.5—9.3 mm. long, pubescent like the herbage with white, partly fuscous, or partly black hairs, the subsymmetric disc 0.7—1.6 mm. deep, the submembranous, campanulate tube 3.5-5.9 mm. long, (2) 2.3-4.5 mm. in diameter, the broadly subulate or obtusely triangular teeth 0.5—3.6 mm. long, the orifice often oblique, the whole becoming papery, marcescent unruptured; petals ochroleucous, pinkish-white, lilac, or pink-purple, the wing-tips often paler than the banner, the color fugacious on drying; banner recurved through 50-80°, obovate- or ovate- cuneate, sometimes subrhombically so, notched, 8.3-16.2 mm. long, 5.3-10.2 mm. wide; wings 7-15 mm. long, the blades narrowly oblong-elliptic, oblong, or oblanceolate, obtuse or erose-emarginate, both gently incurved but the left one more abruptly so and its inner margin infolded; keel 7.3-13.8 mm. long, the blades lunately lanceolate or half-ovate, gently incurved through 50-95° to the narrowly triangular, acute or subacute, often slightly porrect apex; anthers (0.4) 0.450.75 (0.8) mm. long; pod pendulous, stipitate, the slender stipe 2-9 mm. long, the bladdery-inflated, balloon-shaped body 1.5-6 cm. long, 1-2.5 (when pressed, apparently to 2.9) cm. in diameter, widest shortly below the obtuse, subsym- metric, beakless apex, tapering downward into the stipe, terete or shallowly sulcate along the subfiliform sutures, the papery, usually brightly red- or purple-mottled, glabrous or strigulose valves becoming stramineous (between the blotches), lustrous, delicately reticulate, not inflexed, the funicular flange 0.2-0.8 mm. wide; ovules (13) 15-30 (37); seeds brown, greenish- or purplish-brown, sometimes purple-speckled, dull, 2-3.3 mm. long.
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Discussion
The balloon milk-vetch is a species of wide, discontinuous distribution which has become adapted to a variety of environmental and climatic conditions. In the process it has evolved into a number of geographic races often difficult to define in exact contrasting terms, but as a whole well marked by characters of stature, growth-habit, pubescence, and size of the flowers. The pod of A. Whitneyi remains essentially uniform throughout the species, although it is quite variable in size and in length of stipe within the limits of each variety. The present account follows, except for some small but important alterations to the key, a revision already published (Barneby, 1950, p. 204-7).