Astragalus asymmetricus E.Sheld.
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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(2): 597-1188.
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Family
Fabaceae
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Scientific Name
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Type
"California, Douglas."—Holotypus, so labeled, NY (herb. Torr.)! isotypi, BM, G, K, OXF!
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Synonyms
Astragalus leucophyllus Torr. & A.Gray, Phaca leucophylla (Torr. & A.Gray) Hook. & Arn., Tragacantha leucophylla (Torr. & A.Gray) Kuntze, Astragalus leucopsis var. leucophyllus (Torr. & A.Gray) M.E.Jones, Astragalus leucopsis var. asymmetricus (E.Sheld.) M.E.Jones
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Description
Species Description - Tall, stout perennial, with woody a taproot and at length basally indurated stems, densely silky-strigulose throughout with fine, appressed or narrowly ascending and (especially upward) a few longer, loosely ascending or spreading straight or largely straight hairs up to 0.4-0.65 (0.75) mm. long, the herbage greenish- cinereous or, late in the season, canescent, the leaflets equally pubescent on both sides or a trifle more densely so above than beneath, exceptionally glabrous above; stems erect or ascending in well-furnished clumps, 5-12 dm. long, striate, hollow and purple-tinged proximally or nearly throughout, branched or spurred at 1- several nodes preceding the first of (1) 3-12 peduncles, commonly zigzag above; stipules scarious, pallid, or stramineous, 2-14 mm. long, dimorphic, the lowest amplexicaul and connate through half their length or more into a bidentate sheath (this often ruptured in age by expansion of the stem), the median and upper ones shorter, deltoid-acuminate from a broad, semiamplexicaul base, fragile and often deciduous in age, all thinly pubescent dorsally; leaves (5) 7-17 (20) cm. long, shortly petioled or the uppermost subsessile, with rather stiff, commonly recurving rachis and (17) 21-35 linear, linear-oblong, -elliptic, -lanceolate, or -oblanceolate, obtuse and mucronulate or shallowly emarginate, flat or loosely involute, dorsally carinate leaflets (3) 6-26 mm. long; peduncles stiffly erect, 6-24 cm. long, the lower ones surpassing, the uppermost about equaling the leaf; racemes loosely 15—45-flowered, the flowers early nodding, the axis much elongating, (5) 7—17 cm. long in fruit; bracts papery-scarious, narrowly triangular to linear-lanceolate, 1.5—4 mm. long, in age fragile and often deciduous; pedicels densely white-silky-pilosulous, at anthesis strongly arched or distally bent outward and downward, 1.2-2.2 mm. long, in fruit thickened, erect or narrowly ascending, straight or nearly so, 3.5—5 mm. long; bracteoles 0—2, minute when present; calyx (6.5) 8-11.4 mm. long, densely white-silky-strigulose, the slightly to strongly oblique disc 1.2-2 mm. deep, the deeply campanulate, basally turbinate or obliquely truncate tube 5-7.2 mm. long, 3-4.3 mm. in diameter, the lance-subulate teeth (1.5) 2-4.2 mm. long, the whole becoming papery, persistent unruptured; petals ochroleucous, immaculate, little graduated; banner very gently recurved distally but the distal margins abruptly folded back in late anthesis, broadly spat- ulate, entire or shallowly emarginate, 12.6-17.6 mm. long, 7-9 mm. wide; wings (0.2 mm. longer to 1.2 mm. shorter) 12.8-16.4 mm. long, the claws 7-9.7 mm., the narrowly oblong-oblanceolate, obtuse, erose-undulate, or obscurely emarginate, nearly straight blades 6.5-8.2 mm. long, 2.3-3.4 mm. wide; keel 11.5-14.7 mm. long, the claws 7-9.5 mm., the half-obovate blades 5-6.1 mm. long, 2.6-3.3 mm. wide, abruptly incurved through 90-95° to the bluntly deltoid apex; anthers 0.65-0.9 mm. long; pod loosely spreading or pendulous, stipitate, the slender, downwardly or sigmoidally arching stipe 1.4-4 cm. long, the very obliquely ovoid- ellipsoid or half-ovoid, bladdery-inflated body (2) 2.5-4.3 cm. long, 1.3-1.8 (or when pressed seemingly up to 2) cm. in diameter, broadly to narrowly cuneate at base, contracted distally into a deltoid or triangular-acuminate, laterally flattened beak 4—14 mm. long, the body a trifle compressed laterally, esculate, the sutures filiform, the ventral one slightly convex, straight, or gently concave- arcuate, the dorsal one gibbous-convex, the thin, pale green, sparsely strigulose valves becoming papery, stramineous, lustrous, finely reticulate, inflexed as a rudimentary septum 0.1—0.3 mm. wide, the funicular flange (at the middle of the pod) 1.5-2.5 mm. wide; dehiscence apical, through the beak; ovules (16) 18-30; seeds ochraceous or light brown, smooth but dull, 2.1—2.8 mm. long.
Distribution and Ecology - Dry grassy hills, fields, roadside banks, and rolling plains, 200—2500 feet, common and locally plentiful in the inner South Coast Ranges of California and adjoining Great Valley, from western Kern County and head of Salinas Valley in San Luis Obispo County north through the hill-country east of San Francisco Bay to Solano County.—Map No. 110.—April to July, occasionally again in fall.
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Discussion
The horse milk-vetch, A. asymmetricus, is a bold, handsome plant notable among the bladdery-fruiting astragali of cismontane California for the length of the stipe, which may attain the extraordinary length of four centimeters. Next to the much smaller-flowered, diffuse or prostrate A. Douglasii, the species is the commonest astragalus of arid grasslands below 2000 feet in the inner Coast Ranges, whence it extends onto the floor of the Salinas and Great Valleys, here and there forming extensive colonies, especially on overgrazed land. The eastern margin of its range overlaps that of the habitally similar A. oxyphysus, which is, however, easily distinguished by its softer, villosulous vesture, more deeply campanulate or cylindric calyx-tube, more strongly graduated petals, and especially by the pod. This is technically sessile, deciduous from a gynophore much shorter than the stipe of A. asymmetricus, and although bladdery-inflated, at the same time strongly compressed laterally and bicarinate by the salient sutures. In San Benito County occurs a rare variant of A. curtipes in which the body of the pod is quite like that of A. asymmetricus in form; but this is ordinarily a greener plant, with shallower calyx-tube and a short, straight gynophore in place of the long, flexuous or sigmoidally arched stipe. The nearest relative of the horse milk-vetch is A. trichopodus var. lonchus, an essentially coastal astragalus which has been traced northward on the mainland no farther than Point Mugu in Ventura County. Here again the pod is similar in shape and texture, but the stipe is shorter (0.5-1.5 cm. long), the funicular flange much narrower, and the stipules, with very rare exceptions, are all free. The flower of A. asymmetricus is very characteristic because of the subequally long petals which present a blunt (or as Jones called it "stubby") appearance, viewed in profile.
The horse milk-vetch or horse loco, as it is often called, is one of the most widely known and feared weeds of the range in the dry inner valleys and hills of California. It is especially attractive to horses, which develop a craving for the plant and once addicted are never really cured. Ernest Twisselmann (personal communication) described the course of loco disease in horses as remarkably similar to narcotic addiction in human beings; if allowed to run its course, it culminates in hallucinations and loss of muscular coordination, and finally a complete neurological collapse, complicated by malnutrition, leads to death. Cattle are less often affected, avoiding the weed when forage is offered, and after periods of sickness may recover. With the mechanization of farming and the obsolescence of the horse as a source of power and locomotion, the problem of A. asymmetricus has become less acute than formerly, but according to Twisselmann attempts to control the horse loco are standard practice on well- managed ranches.
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Objects
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Distribution
California United States of America North America|