CACTUS FAMILY 159 



1. OPtJNTIA Hill. PmcKLY Pear, Cholla, Indian Fifi, Tkke Cactus. 



Intemodes cylindrical; spines covered with a delicate sheath. 



Internodes very fleshy, turgid, easily detached. 1. O. echinocarpa. 



Intemodes less fleshy, not easily detached. 



Fuit dry; seeds angular. 2. O. acanthocarpa. 



Fruit fleshy; seeds not angular. 



Plants tail (Ito 3 meters high); flowers red. 3. O. arborescens. 



Plants low and spreading (less than 1 meter high) . 



Spines yellow; flowers olive-green. 4. O. Davisii. 



Spines white; flowers yellow. 5. O. Whipplei. 



Internodes flat and broad ; spines not covered by a sheath. 

 Piilvinl not densely woolly. 



Fruit dry when mature, usually very spiny. 



Intemodes very fleshy, often terete in section, the terminal one easily break- 

 ing loose. 6. O. fragilis. 

 Intemodes never terete in section, but always much broader than thick. 

 Intemodes somewhat turgid ; spines very long. 7. O. rutila. 

 Intemodes flat; spines medium length. 

 Petals normally yellow. 



Spines stout, dark brownish. 8. O. polyacantha. 



Spines weak, white. 9. 0. Schweriniana. 



Petals red. 



Filaments red. 10. O. rhodantha. 



Filaments yellow. 11. O. xanthostemma. 



Fruit juicy, usually naked or nearly so. 



Intemodes pubescent, always spineless. 12. O. basilaris. 



Intemodes glabrous. 



Internodes often naked or sometimes bearing long, stout spines. 



Intemodes pale, somewhat glaucous. 13. O. humifusa. 



Intemodes deep green. 14. O. Greenei. 



Internodes generally bearing several spines from each areole. 



Spines twisted. 13. O. tortispina. 



Spines not evidently twisted. 



Low and procumbent; internodes 5 to 10 cm. broad. 



16. O. camanchica. 

 Stout and somewhat ascending; intemodes 12 cm. or more broad. 



17. O. utahensis. 

 Pulvinl densely long-woolly. 



Plant erect; one spine deflexed. 18. O. Palmeri. 



Plant prostrate; all spines deflexed. 19. O. rubrifolia. 



2. ECHINOCEREUS Engelm. Hedgehog Cebeus. 



Corolla greenish; ribs of the stem about 13. 1. E. viridiflorus. 



Corolla red or purple; ribs usually less than 13. 

 Ribs of the stem 8-12. 



Flowers scarlet: central spines 2—7. 



Central spines all terete; flowers 4-6 cm. long, yellowish inside. 



2. E. aggregatus. 

 Lower central spine quadrangular; flowers 8-10 cm. long. 3. E. Boemeri. 

 Flowers purple or violet. 



Central spines 4-5, straight. 4. E. Bngelmanni. 



Central spines soUtary, bulbous at the base. 



Central spine terete; radials 12-25 mm. long, the lower stouter. 



5. E. Fendleri. 

 Central spine angular; radials 2-5 cm. long, the lateral ones strongest. 



6. B. mojavensis. 

 Ribs of the stem 5-7. 



Centra,! spine present, 8 cm. long, angled and grooved; radials 6-8, strongly 



angled. 7. E. goniacanthus 



Centralspine wanting; radials 3— 59, almost terete. 8. E. paucispinus] 



3. ECHINOCACTUS Link & Otto. Hedgehog Cactus, Barrel Cactus. 



stem with definite ridges, not tuberculate. 



Scales of the hypanthlura subulate, copiously woolly in their axils; fruit dry and 

 clothed with wool. 

 Uppermost central spine the broadest; ribs of the stem 15-20. 



1. E. polycephalus. 

 Lowermost central spine the broadest; ribs of the stem 13. 2. 'E. xeranthemoides. 

 Scales of the hypanthium ovate, orbicular, or cordate, not woolly in their axUs; fruit 

 not woolly. 

 One or more of the central spines strongly hooked, neither annulate nor strongly 

 compressed. 

 Central spines except the hooked one, flattened, glabrous. 



3. E. Whipplei. 

 Central spines all terete, pubescent. 4. E. pubispinus. 



On or more of the central spines distinctly annular, strongly broadened, flattened 

 above, slightly if at all hooked. 

 Radial spines 9-13; upper central spine angled. 5. E. cylindraceus. 



Radial spines over 20; upper three spines terete. 6. E. WisUzeni. 



