2l6 
THE CACTACEAE. 
Subtribe 5. CACTANAE. 
One-jointed plants, usually stout, globose to oblong, either solitary’ or cespitose, terrestrial; 
ribs usually straight, their areoles nearly or always spine-bearing; the flower-bearing areoles form¬ 
ing a terminal eephalium 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. r. 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: 24.1. 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 man}’ segments, 
usually white or pinkish; fruit small, naked; seeds black, roughened. 
Fig. 228.—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 eephalium, 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 
ty r pe, but these were afterwards combined into D. placentiformis. 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. 
