LOASACEAE. 237 



3. MENTZELIA L. 



i. Mentzelia oligosperma Nutt. On dry prairies, plains and hills from S. D. 

 and Colo, to La. and Tex. ; also in Mex. Alt. 4000-6000 ft. Foot-hills, 

 Larimer Co. ; southwest of Soldier Canon. 



Family 93. CACTACEAE H. B. K. CACTUS FAMILY. 



Stems continuous or not conspicuously jointed ; leaves obsolete ; spines not 



barbed ; spine-bearing and flower-bearing areolas distinct. 

 Flowers not arising from the tubercles, but from their axils ; ovary naked. 



i. CACTUS. 

 Flowers arising from the tubercles or ribs ; ovary scaly. 



Flowers nearly terminal, i. e,, arising near the areolas which later develop 



spines ; stem never jointed. 2. ECHINOCACTUS. 



Flowers lateral, i. e., arising near the fully developed spine-bearing areolas. 



3. ECHINOCEREUS. 



Stems conspicuously jointed; leaves evident, but deciduous; spines barbed; 

 flowers arising from spine-bearing areolas. 4. OPUNTIA. 



i. CACTUS L. BALL-CACTUS. 



Central spine usually solitary ; corolla greenish. 



Plant simple or nearly so; central spine robust, porrect. i. C. missouriensis. 



Plant cespitose ; central spine often lacking. 2. C. similis. 



Central spines 3-12 ; petals purple. 



Plant usually cespitose, depressed-globose ; central spines 3-4. 



3. C. viviparus. 

 Plant usually simple, ovate to cylindric ; central spines 4-12 (rarely 3). 



4. C. radiosus. 



1. Cactus missouriensis (Sweet) Kuntze. (Mamillaria missouriensis 

 Sweet) On dry plains and hills from S. D. and Mont, to Kans. and Colo. 

 Como. 



2. Cactus similis (Engelm.) Rydb. (Mamillaria similis Engelm. ; M. 

 missouriensis caespitosa S. Wats.) On dry hills from Kans. and Colo, to 

 Tex. "Colorado" (Greene). 



3. Cactus viviparus Nutt. (Mamillaria vivipara Haw.) On dry hills and 

 plains from Neb. and Mont, to Colo. Ft. Collins. 



4. Cactus radiosus (Engelm.) Coulter. On plains from Colo, and Utah 

 to Tex. and Ariz. In Colorado it is only represented by the var. neo- 

 mexicanus (Engelm.) Coulter, lower than the type and with more numerous 

 central spines. '' Colorado " ; Ft. Collins ; Hermosa. 



2. ECHINOCACTUS Link & Otto. HEDGEHOG-THISTLE, CACTUS. 



Stems with tubercles, resembling Cactus in habit. 



Radiating spines 89; central ones 13. i. E. glaucus. 



Radiating spines about 20; central ones 8 10. 2. E. Simpsoni. 



Stems with definite ridges, scarcely tubercled. 3. E. Whipplei. 



1. Echinocactus glaucus K. Sch. In dry places in Colo. Alt. about 6000 

 ft. Mesa Grande on Dry Creek; Gunnison. 



2. Echinocactus Simpsoni Engelm. (Mamillaria Simpsoni M. E. Jones; 

 M. Purpusi K. Sch.) On dry table-lands of Utah and Colo. Alt. 7500-11,000 

 ft. Clear Creek, Sangre de Cristo Pass ; Veta Pass ; Veta Mountain ; Empire ; 

 Dolores. 



