56 



THE CACTACEAE. 



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

 small (2 cm. broad); young ovary bearing brown spines in the axils of the leaves; fruit strongly 

 tuberculate, spineless, 2.5 to 4 cm. long, with a deeply depressed umbilicus, sometimes with only 

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



Type locality: About Zuni, New Mexico. 



Distribution: Northern New Mexico and Arizona to southwestern Colorado and prob- 

 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 : pi. 24, f. 9, 10. 



Figure 66 is copied from the illustration above cited. 



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



Series 4. ECHINOCARPAE. 



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

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

 States, Sonora, and Lower Californja. 



Key to Species. 



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



Fruit long-spiny, strongly tuberculate 16. 0. acanthocarpa 



Fruit short-spiny, little tuberculate ; 17. 0. 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. 0. serpentina 



