6o 



THE CACTACEAE. 





Fig. 71. — Opuntia ciribe. 



Fig. 72. — Opuntia ciribe. X0.8. 



Series 6. IMBRICATAE. 



The typical species are tall, much branched, very spiny. The terminal joints are fleshy and 

 strongly tuberculate, the tubercles large and flattened laterally. The fruit is either smooth or 

 strongly tuberculate. We recognize 8 species, natives of Mexico and southwestern United States. 



Key to Species. 



Joints cylindric; tubercles much flattened laterally. 

 Fruit smooth or but slightly tuberculate. 



Branches very stout, 5 cm. thick or more 22. O. cliolla 



Branches relatively slender, 2 cm. thick or less. 



Plant glaucous ; spines 4 at an areole 23. 0. calmalliana 



Plant not glaucous; spines more than 4 at an areole 24. 0. versicolor 



Fruit manifestly tuberculate. 



Tall species, up to 2 or 4 meters high. 



Flowers small; petals 1.5 cm. long 25. 0. lloydii 



Flowers large; petals 2 to 3 cm. long 26. 0. imhricata 



Low species, 6 dm. high or less. 



Flowers yellow 27. 0. lunicata 



Flowers rose-colored 28. O. pallida 



Joints clavate; tubercles not much flattened laterally 29. O. molesla 



22. Opuntia choUa Weber, Bull. Mus. Hist. Nat. Paris i : 320. 1895. 



Usually tree-like, i to 3 meters high, with a definite trunk 7 to 15 cm. in diameter; trunk 

 very spiny at first and becoming more spiny each year for some time, but in age spineless and 

 developing a smooth, brownish yellow bark; top of plant often dense and broad; joints often in 

 whorls, horizontal, pale, with large compressed tubercles; spines usually numerous, more or less 

 porrect, covered with loose brownish sheaths; glochids numerous, yellow; flowers rather small, 

 3 cm. broad, deep purple; fruit often 4 to 5 cm. long, usually proliferous, often in long chains of 8 

 to 12 individuals or forming compound clusters; seeds numerous, very small, often abortive. 



