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



33. Joints rather weakly armed; spines less than 2.5 cm. long, the 

 sheaths not conspicuous; plant 1 to 2 m. high; flowers yellow, 



red, or rarely purple 30. O. thornberi. 



33. Joints strongly armed; spines numerous, the principal ones 

 more than 2.5 cm. long, conspicuously sheathed; plant 1.5 



to 3 (rarely up to 5) m. high 31. O. acanthooarpa. 



30. Fruit persisting for more than 1 season, fleshy; plant 2 to 4 m. high (34) . 



34. Mature fruit evidently tuberculate, solitary; joints 1.5 to 3 cm. 



thick; tubercles 6 to 15 mm. long; spines 10 to 15 mm. long; 



flowers purple, occasionally red or yellow 34. O. spinosior. 



34. Mature fruit slightly or not at all tuberculate (35). 



35. Joints readily detached, impenetrably armed, 3 to 5 cm. thick, 

 pale green; spines and sheaths straw-colored; fruits proliferous, 

 suspended in chainlike clusters ; flowers pink j _ 32. O. fulgida. 

 35. Joints not readily detached, very spiny but not impenetrably 

 armed, about 2.5 cm. thick, elongate, usually purplish; spines 

 dark-colored; fruits solitary or sparingly proliferous; flowers 

 commonly purple, occasionally red or yellow. 



33. O. VERSICOLOR. 



1. Opuntia basilaris Engelm. and Bigel. in Engelm., Amer. Acad. 



Arts and Sci. Proc. 3: 298. 1856. 



Mohave, Yavapai, Maricopa, and Yuma Counties, up to 3,000 feet, 

 March and April, type from Mohave County. Southern Utah to 

 southern California, Arizona, and Sonora. 



Beavertail cactus (pi. 25). The typical form is a handsome plant 

 with large, velvety, ash-gray joints and magenta flowers with some- 

 what crispate perianth segments. 



2. Opuntia aurea Baxter, Cactus and Succulent Jour. 5: 489. 1933. 

 Northern Mohave County, type from Pipe Springs, about 5,000 



feet, May. Eastern California, southern Nevada, southwestern Utah, 

 and Arizona. 



The flowers are either yellow or pink. The fruit has not been seen 

 by the writers, although in the key to species it is assumed to be dry 

 and spineless. An amazing variety of forms was observed at the 

 type locality. The areoles are not always deeply depressed and the 

 joints vary greatly in size, thickness, and color. Plants with spines 

 along the margin and on the upper areoles are not uncommon. 

 Opuntia rhodantha occurs at Pipe Springs and it seems probable that 

 some of the variant forms are the result of natural crossing. 



3. Opuntia fragilis (Nutt.) Haw., Sup. PL Succ. 82. 1819. 



Cactus fragilis Nutt,, Gen. PI. 1: 296. 1818. 



Apache County to Coconino County, 6,500 to 7,500 feet, with 

 pines, June. Wisconsin to British Columbia, south to Texas and 

 Arizona. 



4. Opuntia polyacantha Haw., Sup. PL Succ. 82. 1819. 



Apache County to Coconino County, 6,000 to 7,200 feet, June. 

 Alberta to North Dakota, Washington, Texas, and Arizona. 



A widely ranging and variable species. The var. trichophora 

 (Engelm. and Bigel.) Coult,, distinguished by long flexuous bristle- 

 like spines at the base of old joints, is not uncommon, in the north- 

 eastern part of the State. The typical form appears to be rare in 

 Arizona. 



