OPUNTIACEAE 813 



6. Cactus Missourten sis (Sweet) Kuntze. Steins usually simple, subglobose, 

 about 3-5 cm. high, with cylindric-ovoid tubercles 12-14 mm. long, these slightly 

 grooved: spines narrow; radials 13-17, whitish, bristle-like, 8-10 mm. long, straight; 

 central solitary, stouter, 10-12 mm. long, puberulent, or often wanting: flowers yel- 

 low to reddish, mostly 2-4 cm. long : stigmas 2-5 : fruits subglobose, 6-8 mm. in 

 diameter, scarlet: seeds subglobose, about 1 mm. in diameter or a little smaller, 

 black, pitted. 



In dry soil and on prairies, South Dakota to Colorado, Kansas and Texas. 



7. Cactus similis (Engelm.) Small. Stems proliferous, forming tufts 2-3 dm. 

 broad: tubercles crowded, often in 8 rows, with woolly axils: spines various; radials 

 12-15, white, straight, puberulent, very slender, commonly equal; central solitary, 

 stouter or wanting: flowers yellow or reddish yellow, 2.5-5 cm. long: stigmas 5: 

 fruits globose-obovoid, scarlet, 3.5-5 mm. long: seeds subglobose, 1.5 mm. to fully 2 

 mm. in diameter, conspicuously pitted. [Mamillaria similis Engelm.] 



In dry soil, Kansas to Colorado and Texas. 



8. Cactus robustior (Engelm.) Small. Stems usually simple, obovoid, 3.5-5 

 cm. high, with the loosely arranged tubercles often in 13 rows: spines various; radials 

 10-12, rather stout, 6-16 mm. long; central solitary, stout, about 12 mm. long: 

 flowers pale yellow, 3.5-4 cm. long and broad: stigmas 7-8': fruits globose-obovoid, 

 6-10 mm. long: seeds about 2 mm. long. [Mamillaria similis var. robustior Engelm.] 



In sandy soil, Oklahoma and Texas. 



9. Cactus sulcatus (Engelm.) Small. Stems proliferous, forming tufted masses 

 several dm. high: tubercles oblong-ovoid, spreading from dilated bases: spines 

 various; radials 8-12, straight, gray or whitish; central solitary, longer, slightly 

 recurved: flowers yellowish, fully 5 cm. long and broad: stigmas 7-10: fruits green- 

 ish, oblong: seeds about twice as long as broad, nearly smooth. [Mamillaria sulcata 

 Engelm.] 



In dry soil, Texas. 



10. Cactus radiosus (Engelm.) Coulter. Stems oblong-ovoid or cylindric, 5-12 

 cm. high, simple or sparingly proliferous: spines various; radials 20-30, white, or 

 darker near the apex, 6-8 mm. long, conspicuously unequal, straight; centrals 4-5, 

 stouter than the radials, 8-12 mm. long, yellowish tawny, the lower shorter than the 

 upper: flowers violet or deep purple, 3.5-5.5 cm. long and broad: fruits oval, about 

 2 cm. long, green: seeds narrowly obovoid, fully 2 mm. long, yellowish or brown, 

 pitted. 



In dry soil, southern Texas to New Mexico and adjacent Mexico. 



11. Cactus Neo-Mexicanus (Engelm.) Small. Stems subglobose to ovoid or 

 cylindric, 3.510 cm. high, simple or proliferous near the base: spines various; radials 

 12-40, slender, mostly 6-9 mm. long; centrals 3-12, purple: flowers purplish, flat, 5-6 

 cm. broad: fruits oval-obovoid, 2 cm. long: seeds oblong-obovoid, about 1.5 mm. 

 long, nearly smooth. [Mamillaria vivipara /3 radiosa Neo-Mexicana Engelm.] 



In dry soil, Kansas to Utah, Oklahoma, Texas, Arizona and adjacent Mexico. 



2. ECHINOCACTUS Link & Otto. 



Plants globular oblong or cylindric, with spine-bearing ribs or vertical or spiral 

 rows of tubercles. Flowers arising from areolae on the tubercles near the areolae 

 which later produce spines. Style columnar. Fruit fleshy or dry, with scales or 

 tufts of bristles. 



Spines, especially the central, very slender, terete. 



Ribs less than 10 : central spines 4. 1 . E. Schottii. 



Ribs more than 12: central spines 13. 2. E. setispinus. 



Spines, especially the central, stout, flattened. 



Central spines straight or slightly curved. 3. E, Texensis. 



Central spines hooked. 



Radial spines mostly 8: central spines 5-15 cm. long: flowers 2.5-3.5 



cm. long. 4. E. Wrightii. 



Radial spines 1012: central spines 25-35 mm. long: flowers 5-7 cm. 



long. 5. E. Muhlenpfordtij. 



1. Echinocactus Sch 6tt (Engelm.) Small. Stems ovoid or cylindric-ovoid, 

 10-15 cm. high, 5-7.5 cm. thick, usually solitary, the ribs often 8, oblique: spines all 

 or some variegated with red and white; outer 15-17 radiant, straight, variable in 

 length; central usually 4, of 2 kinds; uppermost 3-4 cm. long, flat above, keeled 

 beneath, straight or slightly curved, the three lower ones much shorter, nearly terete 



