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 Cafion. 



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. ECHINOCEEEUS. 



Stems conspicuovisly 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. 1 . 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. 



I. Cactus missouriensis (Sweet) Kuntze. {Mamillaria missouriensis 

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

 Como. 



■z. 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 8-9; central ones 1-3. 1. E. glaucus. 



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



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



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

 ft. — Mesa Grande on Dry Creek; Gunnison. 



^. 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. 



