2 BULLETIN 969, U. S. DEPARTMENT OF AGRICULTUEE. 



Asclepias galioides, the whorled milkweed of Colorado, Utah, Arizona, 

 and New Mexico, is one of the most poisonous of the weeds affecting 

 our livestock, and under some circumstances causes very heavy 

 losses. Especial interest, therefore, attaches to the other closely 

 allied plants. The whorled milkweeds form a very distinct group of 

 the milkweed family, Asclepiadacese, being easily recognized by the 

 narrow leaves which are frequently arranged in a whorled manner. 



The number of species of these plants depends upon the opinions 

 of the botanists who study them, but for our purposes four may be 

 recognized which have a fairly definite geographical range. The 

 relationships of these species are briefly characterized by Eggleston in 

 Bulletin 800, United States Department of Agriculture, pages 5 and 6 : 

 Asclepias galioides is found in Colorado, Utah, Arizona, and New 

 Mexico, west of the Continental Divide, and so far as known does not 

 extend west of Utah; Asclepias pumila grows in the plains east of 

 the Rocky Mountains ; Asclepias verticillata is found in the Mississippi 

 Valley, and eastward; Asclepias mexicana is a western species, 

 being especially abundant in California. 



In Bulletin 942, United States Department of Agriculture, Asclepias 

 pumila and Asclepias verticillata var. geyeri were shown to have 

 properties similar to those of Asclepias galioides, but differing in 

 degree. It is evidently a matter of considerable importance, as well 

 as of interest, to find out definitely the character of Asclepias mexicana, 

 which has been frequently reported in California as a sheep-poisoning 

 plant, although published statements are very few. 



Chesnut (1898) says that it is reported from California that sheep 

 and calves were poisoned by eating the growing plant, and cows by 

 eating hay containing it. 



Pammel (1910) quotes the statement of Chesnut. 



Jepson (1911) states that it is said to poison cattle. 



Hall (1912) says: 



It is much dreaded by sheepmen on hot days, when they are obliged to drive their 

 flocks over dry districts, where there is little other vegetation and no water. Under 

 these conditions the sheep are tempted to eat the milk\veed, which contains an active 

 poison and causes many deaths. This is sometimes prevented by cutting the plants 

 down a few days before the sheep are driven through, the object being to dry the 

 herbage and so render it less tempting. 



Hall and Yates (1915) speak of the three species, Asclepias mexicana, 

 Asclepias eriocarpa, and Asclepias speciosa, as being equally poisonous, 

 treat of their distribution, and give symptoms as reported to them. 

 These symptoms do not correspond to those appearing in sheep 

 poisoned by Asclepias mexicana. It may be noted, too, that the 

 authors of this bulletin have not only failed to get any clear evidence 

 of poisoning by Asclepias speciosa, but have also failed experimentally 

 to poison animals by it. 



