692 MISC. PUBLICATION 42 3, U. S. DEPT. OF AGRICULTURE 



20. Plant more or less glaucous; leaf blades thin, oblong or 

 elliptic, 2 to 3 times as long as wide, sessile and often 

 cordate-clasping; peduncles nearly as long as to longer 

 than the leaves; corolla lobes 8 to 10 mm. long. 



20. A. ELATA. 



20. Plant not glaucous; leaf blades thick, ovate, obovate, or 

 nearly orbicular, usually not more than 1.5 times as long 

 as wide, very short-petioled; peduncles much shorter than 

 the leaves; corolla lobes 7 to 8 mm. long. 



21. A. LATIFOLIA 



1. Asclepias albicans S. Wats., Amer. Acad. Arts and Sci. Proc. 24: 59." 



1889. 



Western Maricopa County and Yuma County, 1,000 feet or lower, 

 dry granitic or volcanic slopes, March. Southwestern Arizona, 

 southeastern California, and northwestern Mexico. 



Stems as many as 50 from 1 root, reaching a height of 3 m, (10 

 feet) and a diameter of 2 cm. 



2. Asclepias subulata Decne. in DC, Prodr. 8: 571. 1844. 

 Mohave, Gila, Maricopa, Pinal, and Yuma Counties, 3,000 feet 



or lower, locally abundant on dry slopes, mesas, and plains, April to 

 October. Southern Arizona, southeastern California, and north- 

 western Mexico. 



The sap contains an appreciable quantity of rubber, latex sometimes 

 constituting as much as 6 percent of the dry weight. A. subulata 

 and A. albicans are extreme xerophytes. 



3. Asclepias tuberosa L., Sp. PL 217. 1753. 



Apache County to Coconino County, south to Cochise and Pima 

 Counties, 5,000 to 8,000 feet, mostly in open places in pine forests, 

 May to July. Throughout much of the United States. 



Butterfly weed, pleurisy-root. The plant is very showy in flower 

 and is notable in the genus in not having milky sap. The flowers are 

 normally orange red, but vary to pale orange or even yellow. The 

 roots are said to be used locally in treatment of affections of the lungs. 



4. Asclepias linifolia H. B. K, Nov. Gen. et Sp. 3: 190. 1819. 



• Huachuca Mountains (Cochise County), Sycamore Canyon near 

 Ruby (Santa Cruz County), Santa Catalina Mountains (Pima 

 County), 4,000 to 5,000 feet, June and July. Southern Arizona and 

 Mexico. 



The identification of the Arizona specimens as A. linifolia is perhaps 

 questionable. 



5. Asclepias galioides H. B. K., Nov. Gen. et Sp. 3: 188. 1819. 

 Apache County to Coconino and Yavapai Counties, south to Cochise 



and Santa Cruz Counties, 4,000 to 7,000 feet, open plains and mesas, 

 common at roadsides, June to August. Kansas and Colorado to 

 Texas, Arizona, and northern Mexico. 



Horsetail milkweed. Very poisonous to livestock, especially to 

 sheep, but fortunately the plant is unpalatable and eaten only in 

 absence of better liked forage. This dangerous weed should be eradi- 

 cated from pastures and ranges wherever practicable. 



6. Asclepias macrotis Torr., XL'S, and Mex. Bound. Bot. 164. 1859. 

 Chiricahua, Swisshelm, and Mustang Mountains (Cochise County), 



about 6,000 feet, June and July. Western Texas to southeastern 

 Arizona. 



