238 CACTACEAE. 



3. Echinocactus Whipplei Engelm. & Big. On dry plains from Colo, and 

 Utah to N. M. and Ariz. In Colorado has only been found the var. spinosior 

 Engelm. with more numerous, 9-11, radiating spines. La Plata Valley; 

 Mesa Verde. 



3. ECHINOCEREUS Engelm. CEREUS. 



Ribs about 13; corolla greenish or yellowish. i. E. viridifiorus. 



Ribs 5-12; corolla red or purple. 



Plant light green; corolla violet-purple; central spine i, terete, nearly black, 



curved above. 2. E. Fendleri. 



Plant dark green ; corolla scarlet (except perhaps in the first). 

 Ribs 5-7. 



Central spine o ; radiating ones 3-5, almost terete. 3. E. paucispinus. 

 Central spine 8 cm. long, angled and grooved ; radiating ones 6-8, strongly 

 angled. 4. E. gonacanthus. 



Ribs 9-1 i. 



Central spines all terete ; flowers 4-6 cm. long, usually yellowish inside. 



5. E. aggregates. 

 Lower central spines quadrangular; flowers 8-10 cm. long. 



6. E. Roemeri. 



1. Echinocereus viridiflorus Engelm. (Ccreus viridifiorus Engelm.) On 

 high plains and hills from Wyo. to Tex. and N. M. Alt. 5000-8000 ft. Tobe 

 Miller's ranch ; Veta Mountain ; Manitou ; Colorado Springs ; near Bouider. 



2. Echinocereus Fendleri (Engelm.) Riimpl. (Cereus Fendleri Engelm.) 

 On dry plains from Colo, and Utah to Tex. and Ariz. " So. Colorado." 



3. Echinocereus paucispinus (Engelm.) Rumpl. (Cereus paucispinus 

 Engelm.) On rocks and limestone hills from Tex. to Colo. Durango. 



4. Echinocereus gonacanthus (Engelm. & Big.) Lehm. (Cereus gona- 

 canthus Engelm. & Big.) On sandy bluffs in Colo, and N. M. Florence; 

 Arboles. 



5. Echinocereus aggregatus (Engelm.) Rydb. (Mamillaria aggregata En- 

 gelm.; Cereus phoeniceus Engelm.) On plains and hillsides from Colo, to 

 Tex. and Ariz. ; also in Mex. Alt. 5000-7500 ft. La Veta ; Badito. 



6. Echinocereus Roemeri (Muhlenf.) Rydb. (Cereus Roemeri Muhlenf. ; 

 C. conoideus Big.) On plains from Colo. (?) to N. M. and Calif. "So. 

 Colorado." 



4. OPUNTIA Mill. PRICKLY PEAR. 



Internodes of stem short, more or less flattened. 



Internodes of the stem oval or orbicular, decidedly flattened. 

 Fruit fleshy and juicy, spineless or nearly so. 



Spines none, or a solitary strong one reflexed and 1-2 small ones at its 



base, all white or gray. i. O. mesacantha. 



Spines 1-8, not very unlike in length. 

 Spines not twisted. 



Spines 1-3, brownish; internodes orbicular or obovate, 11-15 cm. wide. 



2. O. camanchica. 

 Spines 5-7, white or gray ; internodes oblong, 5 cm. long and 3.5 cm. 



wide. 3. O. Schweriniana. 



Spines twisted, 3-5, white; internodes 13-17 cm. long and about as wide. 



4. O. tortispina. 

 Fruit dry and usually with spine-bearing areolas. 



Corolla yellow. 5. O. polyacantha. 



Corolla red. 



