576 CACTACEAE 



Internodes generally bearing several spines from each areole. 



Spines twisted. 15. O. tortispina. 



Spines not evidently twisted. 



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



16. O. camanchica. 

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



17. O. utahensis. 

 Pulvini densely long-woolly. 



Plant erect; one spine deflexed. 18. O. Palmer I. 



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



1. O. echinocarpa Engelm. A low shrub, 1.5-4.5 dm. high, with numerous 

 spreading branches; internodes ovate, 2.5-6 cm. long, less than 2.5 cm. thick, 

 with ovate crowded areolae, 8-10 mm. long; pulvini with few straw-colored 

 bristles; larger spines about 4, whitish, 18-25 mm. long; smaller ones 8-16, 

 spreading; flowers greenish yellow, 3.5-4 cm. broad; fruit dry, depressed-globose, 

 very spiny. Desert regions: Ariz. s Utah Calif. L. Son. 



2. O. acanthocarpa Engelm. Erect and arborescent, 1.5-2 m. high, with 

 few alternate branches; internodes cylindric, 1-2 dm. long, 2.5 cm. thick; areolae 

 oblong, 18-20 mrn. long; pulvini with short wool and scanty bristles; spines 8-25, 

 spreading in all directions, the inner 2.5-3 cm. long; flowers copper-colored; 

 fruit depressed-globose, with few stout spines. Desert regions: Ariz. s Utah 

 se Calif. Sonora. Son. 



3. O. arborescens Engelm. Erect, arborescent, 1.5-8 m. high, with verti- 

 cillate branches; internodes cylindric, 0.5-1.5 dm. long, 2 cm. thick; areolae 

 oblong, 15-30 mm. long; pulvini short- woolly, but scarcely bristly; spines 8-30, 

 terete, spreading, the inner often 2.5 cm. long; flowers purple, 6-7.5 cm. broad; 

 fruit subglobose, prominently tuberculate, unarmed. TREK CACTUS. Foot-hills 

 and plains: Tex. Colo. Utah Sonora. Son. Submont. 



4. O. Davisii Engelm. Spreading or procumbent, with divaricate branches; 

 internodes slender, narrowed towards the base, 10-15 cm. long, with linear- 

 oblong areolae, 14-16 mm. long; inner spines 4-7, subtriangular, reddish brown, 

 2.5-3.5 cm. long, the lower 5 or 6 slender, 6-12 mm. long; flowers yellowish; 

 fruit ovoid, 2.5 cm. long, spiny. Arid regions: Tex. s Colo. s Calif. Son. 



5. O. Whipplei Engelm. Stem erect, rarely spreading, 2-20 dm. high, with 

 divaricate branches; internodes cylindric, 5-30 cm. long, 1-2 cm. thick, with 

 ovate areolae, 10 mm. long; pulvini sparingly woolly, scarcely bristly; spines 

 short, the longer 1-4 divaricate, 6-18 mm. long, and 2-8 smaller ones deflexed; 

 flowers red; fruit subglobose, lightly tuberculate, unarmed. Desert regions: 

 N.M. s Utah Calif. L. Calif. L. Son. 



6. O. fragilis (Nutt.) Haw. Decumbent; internodes 3.5-5 cm. long, ovate, 

 only slightly compressed or sub terete; pulvini large, white woolly and with few 

 bristles; spines 1-4, divaricate, the uppermost stout, angular, 12-20 mm. long; 

 flowers pale yellow, about 5 cm. broad; fruit ovate, almost naked, about 2.5 cm. 

 long. Plains and hills: B.C. Minn. Wis. Kans. Utah. Plain Submont. 



7. O. rutila Nutt. Stems ascending or diffuse; internodes thick, ovate, 

 5-10 cm. long, 2.5-7.5 cm. broad; pulvini crowded, white- woolly and bristly; 

 spines 3-5, reddish gray, 1-4 cm. long, the central one longer, spreading or 

 declined, the upper erect, the rest reflexed; flowers rose-red or pink; fruit ovate, 

 dry, spinulose, 2.5-3 cm. long. Plains: w Wyo. Calif. Ariz. Son. Submont. 



8. O. polyacantha Haw. Stem prostrate; internodes broadly obovate or 

 orbicular, pale green, 5-15 cm. long, about 12 mm. thick; pulvini densely bristly; 

 spines 5-15, rather stout, 1-5 cm. long, variegated, the 3-5 inner stout, reddish 

 brown, 3-5 cm. long, some deflexed, some spreading; flowers yellow; fruit ovoid, 

 spiny, 2.5 cm. long. 0. missouriensis DC. Plains and prairies: Sask. Wis. 

 Mo. N.M. Utah B.C. Plain. My-Je. 



9. O. Schweriniana K. Schum. Diffuse; internodes oblong, small, only 

 5 cm. long and 3.5 cm. wide; pulvini with brown bristles; spines 7-10, only on 

 the lower side of the pulvini, the larger, only about 1 cm. long, at last all reflexed; 

 flowers 4 cm. broad, yellow or greenish yellow; filaments green or yellow; fruit 

 ovoid. Hillsides: Colo. Submont. 





