CHAPTER XIII 



PRINCIPAL STOCK-POISONING PLANTS 



LOCO PLANTS {Oxytropis and Astragalus) 



Loco plants are members of two genera — Oxytropis and As- 

 tragalus. The most destructive of these plants is the so-called 

 Lambert's, white, stemless, or rattleweed loco {Oxytropis Lam- 

 hertii). It is a perennial herb with stems 12 to 18 inches high, 

 the leaflets of the compound leaves being slender, somewhat 

 hairy, and ohve-green in color. The spikes of flowers are com- 

 monly white, though the corolla is sometimes streaked with 

 purple. As the calyx is sometimes red, a variety of colors is 

 found. The rattling of the pods as one touches them when the 

 seed is mature resembles the sound of a rattlesnake. Accord- 

 ingly the name " rattleweed " is in more or less common use 

 (Fig. 78, colored plate). 



Woolly, purple, or Texas loco {Astragalus mollissimus) is 

 probably the second most destructive species. It is believed 

 to have been the first member of the genus to be recognized as 

 dangerous to livestock. Woolly loco may be distinguished from 

 Lambert's loco by its more leafy stem, its conspicuously hairy 

 and broader leaflets, blunt instead of sharp-keeled, and often 

 by a deeper purple corolla, and shorter, thicker dark-brown 

 pods. (Compare Figs. 78 and 80, colored plate.) 



Distribution and Habitat. — The amount of destructiveness of 

 white loco is due to its very extended range rather than to an 

 extraordinary degree of toxicity. It often grows very abundantly 

 over large areas and is found from the north to the south of the 

 United States, eastward as far as central Minnesota, western 

 Kansas, and western Texas, and westward to western Arizona 

 and western Montana. Woolly loco, as shown in Figure 79, 

 occurs on the west from southeastern Arizona, central Colorado, 

 and southeastern Wyoming, north to South Dakota, east through 



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