LOASACEAE. 
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3. MENTZELIA L. 
1. 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. 
1. 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. 
1. 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. 
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 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. Whxpplei. 
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. 
