56 



THE CACTACEAE. 



loneest about 2 cm. long, dark brown, covered with lighter colored papery sheaths; flowers yellow, 

 sr^fll (2 cm broa^ ; young ovary bekring brown spines in the axils of the leaves; fruit strong y 

 tXrculatt s^nelessf 2.5 to 4 cm. long, with a deeply depressed umbihcus, sometimes with only 

 one seed but usually many; seeds small, 4 cm. broad, smooth. 



^ < 







Mexico 



Distribution: 



Mexico 



ably southern Utah. Also reported by Coulter in southern California, Lower California, 

 and Sonora, but not to be expected there. 



Illustration: Pac. R. Rep. 4 : pl- 24, f-^9. lo- 



■picnirp 66 is cooied from the illustration above cited. 



[ ■ ■ 



Fig. 67. — Opuntia acanthocarpa in the foreground. Photograph by MacDougal. 



Series 4. ECHINOCARPAE. 



V- 



Dry-fruited, rather stout-jointed, bushy or depressed species, the areoles bearing several 

 the flowers red, yellow, or yellowish. Four species, inhabiting the southwestern United 



spines, 



States, Sonora, and Lower Californja. 



Key to Species. 



■i 



Tubercles elongated, 2 to 3 times as long as wide. 



Fruit long-spiny, strongly tuberculate 16. O. acanthocarpa 



Fruit short-spiny, little tuberculate 17. O. parryi 



Tubercles short, less than twice as long as wide. 



Spines with white or straw-colored sheaths 18. O. echinocarpa 



Spines with yellow-brown sheaths 19. O. serpentina 



