KEY TO THE ARBORESCENT SPECIES 

 OF CACTACEAE 



1 . Branches and stems columnar, ribbed, not tuberculate, continuous; 

 areoles (growing centers) without glochids (minute bristles); leaves 

 spinelike; tube of flower elongated; seeds dark-colored; spines not 

 barbed; a tree often 50-60 feet high; the state flower of Arizona 



• Cereus 



giganteus, Engelm. [Carnegiea gigantea (Engelm.) B. & R.]; Saguaro. 



1. Branches and stems slender, columnar, tuberculate, conspicuously 



jointed; areoles with both glochids and spines; leaves small and 



fleshy on young parts; tube of flower short; seed light-colored; 



spines retrorsely barbed ; small plants not over 1 5 feet high Opuntia. 



2. Tubercles of branches broad, full and rounded below areolae; 



flowers pink or purple; fruit sparingly spiny or without spines. 



3. Flowers pink; fruit green, proliferous (one growing from 



another), usually spineless; joints pale olive-green, readily 



detached, freely falling, their tubercles broad and ovoid; 



spines yellow Optuntia fulgida Engelm. ; Cholla. 



3. Flowers purple; fruit yellow, rarely proliferous, spiny; joints 

 green or purple, not readily detached, persistent, their 



tubercles elongated; spines white to red-brown 



Opuntia spinosior (Engelm.) Toumey ; Tasajo. 



2. Tubercles of branches narrow, high and flattened laterally. 

 Flowers purple, or green tinted with red or yellow. 



4. Fruit smooth or but slightly tuberculate, spiny, green; 

 ^ branch tubercles V2" long; spines 5-11, Yq" long or less, 



dark red-brown; flowers green, tinted with red or yellow. . . 



Opuntia versicolor Engelm. ; Staghorn Cholla. 



4. Fruit manifestly tuberculate, naked, yellow; branch tuber- 

 cles H" long; spines 8-30, ^-IH" long, brown; flowers 



purple 



Opuntia imbricata (Haw.) DC. {Opuntia arborescens Engelm.); 

 Cane Cactus. 



fS25] 



