Astragalus mollissimus Torr. var. mollissimus
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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
"On the Platte."—Holotypus, collected by Dr. Edwin James, assistant surgeon U.S.A., on Long’s Expedition in 1820, NY! isotypus (a pod), GH!
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Synonyms
Astragalus simulans Cockerell, Astragalus mollissimus f. flavus McGregor
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Description
Variety Description - Relatively stout and robust, subacaulescent or commonly short-caulescent, the stems 1.5-14 cm. long, the internodes all concealed by imbricated stipules or 1—few developed and up to 4 cm. long, the herbage densely silky-tomentose, the longest, narrowly ascending or spreading hairs up to 1—2.5 mm. long, the vesture ultimately becoming rusty; stipules large and conspicuous, (5) 7—17 mm. long; leaves (7) 10-20 (25) cm. long, with 15-27 (33) oval, ovate, or obovate and obtuse, sometimes rhombic-elliptic and subacute leaflets 5—22 mm. long; peduncles 6—21 cm. long; racemes oblong and rather dense at early anthesis, (10) 15-40- flowered, the axis elongating, (2) 4—17 cm. long in fruit; calyx (8.8) 10.5—14 mm. long, the tube 6.8-9.5 mm. long, 3.4-4.5 mm. in diameter, the teeth (2) 3-5 mm long; petals yellowish suffused with dull lavender, or pinkish, or pink-purple (exceptionally "yellow" in fma. flavus); banner (16) 17.5—21.5 mm. long, 7.2—10.5 mm. wide; wings 15.5-21 mm. long, the claws 7.3-10.8 mm., the blades 9.4-11.7 mm long, 2.3-3 mm. wide; keel (14) 14.5-18 mm. long, the claws (7.5) 8.5-11 mm., the blades 7.4-9 mm. long, 2.9-3.4 mm. wide; pod narrowly oblong-ellipsoid to lance-ellipsoid, 1.4-2.4 cm. long, 4-7 mm. in diameter, shallowly crescentic or abruptly incurved near the middle through ± 90º, contracted distally into a short but evident, conical or deltoid-acuminate, compressed, unilocular beak, the valves commonly glabrous, almost as often glabrous except for the puberulent or hispidulous apex, rarely puberulent or even shortly villosulous throughout; ovules 26-37.
Distribution and Ecology - Prairies, plains, valley floors, stony mesas and fallow fields in alluvial loams, loess, or on outcrops of shale, limestone or sandstone, most abundant where vegetation (due either to site or overgrazing) is low and sparse, widespread and locally abundant between 1700 and 6000 feet over the western Prairie States, ascending in New Mexico into dry pine woods up to 7000 feet, western and southcentral Nebraska and southeastern Wyoming to western Oklahoma, northwestern Texas, and the Pecos and Rio Grande Valleys in central and southeastern New Mexico.—Map No. 97.—Late April to July, sometimes again in fall.
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Discussion
The woolly locoweed, var. mollissimus, a common and justly feared stock-poison of the Prairie States lying between western Nebraska and the Texas Panhandle, is a rather handsome plant. Although all specimens are technically caulescent, the stems are short and densely leafy, so that the silvery-gray foliage is tufted into low, mounded clumps. The peduncles, commonly appearing scapose or nearly so, are incurved-ascending when the flowers are in bloom, but become prostrate and radiate from the root-crown as the fruit is ripening. Within its species the distinctive features of var. mollissimus are the relatively broad calyx and narrow pod, which varies, however, considerably in length and curvature. The ripe fruit disjoints readily from the receptacle, and at dehiscence the gaping unilocular beak provides ready egress to the seeds. The flowers vary from a deep and lively wine-purple through shades of pinkish-lavender to tawny-yellow suffused with lurid purple; a population of plants with truly yellow petals has been described from Barber County, Kansas (fma. flavus McGregor). The latter would key out to var. Coryi but is, in all probability, an independent mutation which has not achieved an independent geographic range. The pod, as I have already mentioned, varies from glabrous to strigulose, when the hairs may cover the whole surface or, more commonly, are concentrated toward the beak. In general a pubescent pod becomes more frequent southward as the range of the vicariant var. Earlei is approached. In southeastern New Mexico and adjoining Texas the vars. mollissimus and Earlei are morphologically confluent, a situation discussed further under the latter heading. In the higher foothills on and about the Pecos-Rio Grande divide in New Mexico, the flowers of the woolly locoweed are a trifle smaller than in the phase prevailing over the open prairies; but this small-flowered form, described as var. simulans, departs too little from the standard var. mollissimus to deserve taxonomic recognition.
The var. mollissimus, which became by the fortunes of history the prototype of its widely dispersed species, is probably a derived form. The approximate geographic center of the woolly locoweed, which coincides with the area of maximum variation, lies in the upper Rio Grande Valley, and it can be assumed that var. mollissimus is a modified offshoot of an ancestor with pubescent pod.
The toxic principle of A. mollissimus was isolated from var. Earlei by Fraps & Carlyle (1936), who labeled it locoine and believed it to be an alkaloid or closely related substance. The varieties of A mollissimus are probably all toxic, especially to horses, and in slightly less degree to cattle, sheep, and goats. We have no experimental data concerning var. Thompsonae, or the Mexican var. irolanus, or the rare vars. mogollonicus, marcidus, and Matthewsii. An informative summary of what was known about loco disease to date may be found in U. S. Department of Agriculture Farmers’ Bulletin No. 1054 (Marsh & al., 1919, revised in 1936 by A. B. Clawson).
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Objects
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Distribution
Wyoming United States of America North America| Nebraska United States of America North America| Colorado United States of America North America| Kansas United States of America North America| Oklahoma United States of America North America| New Mexico United States of America North America| Texas United States of America North America|