2l6 



THE CACTACEAE. 



Subtribe 5. CACTANAE. 



One-jointed plants, usually stout, globose to oblong, either solitary or eespitose, terrestrial; 

 ribs usually straight, their areoles nearly or always spine-bearing ; the flower-bearing areoles form- 

 ing a terminal cephalium composed of a central woody core surrounded by a dense mass of long 

 wool, bristles or both, often elongated; flowers regular, salverform or funnelform, opening in the 

 afternoon or at night; fruit a small naked berry; seeds small. 



We recognize two genera, which are not very closely related. 



Key to Genera. 



Flowers large, white or rose, night-blooming, the limb of many segments 1 . Discocactus 



Flowers small, rose or pinkish, opening in the late afternoon, the limb of few or several segments. . 2 . Cactus 



1. DISCOCACTUS Pfeiffer, Allg. Gartenz. 5: 241. 1837. 



Plants rather small, globose or flattened, ribbed; ribs rather low, tubercled; spines borne at the 

 areoles in clusters, more or less curved; flowers from the center of the plant, appearing from a cepha- 

 lium similar to,""but usually not so prominent as, that of Cactus (Melocactus) ; flowers rather large for 

 the plants, opening at night, with a definite tube, the limb broad, composed of many segments, 

 usually white or pinkish; fruit small, naked; seeds black, roughened. 



Discocactus subnudus. 



Fig. 229. Discocactus alteolens. 



Discocactus was made a subgenus of Echinocactus by Schumann. It is a valid genus, 

 however, confined to eastern South America, although one of the species was originally 

 described, in error, as coming from the West Indies. It is characterized by its plant body, 

 by its cephalium, by its naked fruits, all these suggesting Cactus, and by its flowers which 

 open at night and become limp by the next morning. 



Three species were described by Pfeiffer, of which the first, Discocactus insignis, is the 

 type, but these were afterwards combined into D. placentijormis. Three other described 

 species we believe belong here, only one heretofore referred to Discocactus, the other two. 

 having been described under Echinocactus and Malacocarpus respectively. Three more are 

 here added. 



