WOOTON AND STANDLEY—FLORA OF NEW MEXICO, 437 
Stems short, mostly ovoid, globose, or short-cylin- 
dric, tuberculate; ovary and fruit smooth, 
neither scaly nor spiny........--.-..-...--- 2. MAMILLARIA (p. 447). 
Stems mostly short or long-cylindric, ovoid or occa- 
sionally globose, mostly larger than in the pre- 
ceding genus; tubercles confluent into longi- 
tudinal ridges; ovary and fruit not smooth. 
Ovary and fruit scaly, not spiny; flowers borne 
in the center of the stem at the apex.... 3. Ecxrnocacrus (p. 451). 
Ovary and fruit spiny; flowers borne laterally 
on the stem some distance from the apex. 
Flowers usually brightly colored, red, yel- 
low, or greenish, open during the day; 
stems thick and very spiny, with 6 or 
more ribs........-.---e eee eee eee eee 4, EcHINOCEREUS (p. 454). 
Flowers white, open at night; stems slender, 
4 or 5-ribbed; spines very short and 
inconspicuous...........---.-------- 5, PENIOcEREvS (p. 458). 
1. OPUNTIA Mill. Prickiy pear. 
Perennials with jointed stems, bearing small, terete or conic, fleshy, caducous 
leaves; joints of the stems flattened (‘‘prickly pears” or ‘‘nopales”’), cylindric (‘‘cho- 
llas” or ‘‘cane cacti,’ inpart), or clavate or tumid, smooth to strongly tuberculate; 
leaves usually 1 cm. long or less, to be seen only on the young joints or the young 
ovary; areoles with numerous retrorsely barbed glochids 3 to 15 mm. long and 1 to 
several slender or stout, long or short spines (in one section the spines covered by a 
papery sheath); flowers mostly large, with numerous sepals and petals, very numer- 
ous stamens, and a single thick style with several stigmas; fruit tuberculate or 
smooth, with several to many areoles, these bristle-bearing or sometimes spine- 
bearing, occasionally proliferous, dry or berry-like, with a thick rind (berry-like 
fruits known as ‘‘tunas’’). 
KEY TO THE SPECIES. 
Joints clavate, tumid, or cylindric, not conspicuously flattened. 
Joints clavate or tumid, smooth or tuberculate; plants low, 
30 cm. high or less, spreading; spines without sheaths. 
Joints tumid when fresh and growing, simulating some 
forms of the Platyopuntiae when dry, very small, 
2 to 5 cm. long, 2 to 3 cm. wide and nearly as 
thick; tubercles not conspicuous; spines of the 
fruit merely spreading. 
Joints elliptic-ovate, 3 to 5 cm. long and 2 to 3 cm. 
wide; bristles and spines very numerous, the 
latter white and small.................222--- 3. O. arenaria. 
Joints circular to short-obovate, 2 or 3 cm. long; 
bristles few. 
Spines white or whitish; joints short-obovate.. 1. 0. brachyarthra. 
Spines yellow or brownish; joints nearly orbicu- 
|S 2. O. fragilis. 
Joints clavate (in one species almost cylindric); tuber- 
cles conspicuous, especially in dried specimens; 
spines of the fruit in radiating clusters. 
