812 OPUNTIACEAE 



5. Cactus Texanus (Engelm.) Small. Stems proliferous, forming a tufted mass 

 2.5-6 cm. high, the branches ovoid to globose-obovoid, with tubercles varying from 7-9 

 mm. in length, their axils furnished with wool and twisted bristles : spines various ; radials 

 very numerous in many series, those of the outer series, 30-50, white, hair-like, 12-16 

 mm. long, more or less crisped, those of the inner series, 10-12, shorter, about as long 

 as the outer, puberulent, sometimes varying to yellow ; central spines 5-8, straight, rigid, 

 white or darker above the base, pubescent : flowers yellowish white, 1.5-2 cm. long : fruit 

 club-shaped, 1.5-2 cm. long: seeds 1-2 mm. long, black, shining, pitted. [Mamillaria 

 jwsilla var. Texana Engelm.] 



In sandy soil, Texas and adjacent Mexico. 



6. Cactus Missourie'nsis (Sweet) Kuntze. Stems 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 soli- 

 tary, stouter, 10-12 mm. long, puberulent, or often wanting : flowers yellow to reddish, mostly 

 2-4 cm. long : stigmas 2-5 : fruit subglobose, 6-8 mm. in diameter, scarlet : seeds subglo- 

 bose, 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 : fruit 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. Sterne 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 : fruit globose-obovoid, 6-10 mm. long: seeds about 

 2 mm. long. [Mamillaria similis var. robustior Engelm.] 



In sandy soil, Oklahoma and the Indian Territory to Texas. 



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

 eral 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 : fruit greenish, 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 : fruit 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 cylin- 

 dric, 3.5-10 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 : 

 fruit oval-obovoid, 2 cm. long : seeds oblong-obovoid, about 1.5 mm. long, nearly smooth. 

 [Mamillaria vivapara (3 radiosa Neo-Mexicana Engelm.] 



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



2. ECHINOCEREUS Engelm. 



Plants with ribbed and angled or tubercled ovoid cylindric or columnar nearly con- 

 tinuous stems, the vertical ribs angled or tubercled with numerous spine-bearing areolae. 

 Leaves wanting. Flowers arising from areolae situated just above fully developed, spine- 

 bearing areolae. Hypanthium prolonged beyond the ovary, bearing naked or pubescent 

 scales which are sometimes spiny in their axils. Style filiform. Fruit fleshy. Seeds 

 tuberculate, almost destitute of endosperm. Embryo straight. 



Radial spines 20-30, pectinate. 1. E. caespitosus. 



Radial spines 4-12, not pectinate. 

 A. Joints over 2 cm. thick. 



Central spines usually 2-4. 2. E. dubius. 



Central spines always solitary. 



