144 CACTACEAE 



or dry, spiny or spineless. Seeds covered witli a bony aril, light-colored, flattened. 

 [Greek, named for town in Greece of the same name.] 



A genus of over 2S0 species (over 1,000 names occur in the literature) from British Columbia and Massa- 

 chusetts to the Straits of Magellan. Type species, Cactus Optintia L. 



Joints terete, globose to elongate-cylindric, not flattened, tuberculate; yearly accretions of wood in branches not 

 separated by fleshy tissue. 

 Spines terete, acicular; sheaths deciduous. 

 Fruit dry, not fleshy when mature. 



Tubercles on branches flattened, diamond-shaped, forming regular pattern; branches scarcely fleshy, 

 spines usually solitary. 1. O. ratnosissima. 



Tubercles not flattened nor diamond-shaped, less regularly arranged; branches obviously fleshy; 

 spines usually several. 



Tubercles elongated, 2-3 times as long as wide; branching essentially terminal. 



Fruit-spines in clusters of 8-12, stout; spines densely interlocked, obscuring the younger 

 joints; plants light green. 2. O. acanthocarpa. 



Fruit-spines solitary or few, acicular; spines not interlocked, not covering the joints; 

 plants dark green. 3. O. Parryi. 



Tubercles short, less than twice as long as wide; branching lateral as well as terminal. 



Spines interlocking, obscuring the stems, the sheaths straw-colored; tubercles not flattened; 

 stems not prostrate. 4. O. echinocarpa. 



Spines not interlocking nor obscuring the stems, these and sheaths brownish; tubercles 

 flattened; stems prostrate or scrambling. 5. O. serpentina. 



Fruit fleshy when mature. 



Fruit not proliferous* spine-sheaths pale yellow, roseate, or white, densely interlocking and ob- 

 scuring body of the joints. 6. O. Bigelovii. 



Fruit proliferous; spines and sheaths rusty yellow, scarcely interlocking, not obscuring the joints, 



7. O. prolifera. 



Spines 4-angled, subulate; sheaths caducous. 8. O. Parishii. 



Joints flattened, pad-like, not tuberculate; yearly woody accretions, at least in pads, separated by thin layers of 

 fleshy tissue. 



Plants low, mostly basilate; areoles 1-3 mm. in diameter. 



Areoles, or some of them, containing 1-5 spines; joints not pubescent. 9. 0. Treleasei. 



Areoles containing glochids only, spineless; joints distinctly puberulent. 



Joints thin, 7-30 cm. long; flowers numerous, 6-10 cm. broad. 10. O. basilaris. 



Joints thick, over one- fourth as thick as broad, broadly ellipsoid in cross-section, 2-6 cm. long; 

 flowers few, 4-6 cm. broad. 11. O. hrachyclada. 



Plants 0.5-4 m. high, or if low, not basilate; areoles 2-5 mm. in diameter. 



Fruits dry, not juicy when mature, spiny. 



Joints turgid, nearly or quite as thick as broad, terminal ones easily detached; areoles containing 

 white wool; stems often malted. 12. O. fragilis. 



Joints flattened, not readily detached; areoles containing spines and glochids only, not woolly; 

 stems not matted. 



Spines subulate; areoles distant; only upper areoles of joints spiny. 13. O. hystricina. 



Spines acicular; areoles approximate; all areoles of joints more or less spiny. 



Spines stout, rigid, straight, 1-5 cm. long, some of them deflexed; joints orbicular. 



14. O. polyacantha. 



Spines slender, more or less flexuous, 3-12 cm. long, spreading; joints ovate to oblong. 

 Spines mostly acicular, 3-5 cm. long. 15. O. erinacea. 



Spines bristle-like, flexuous, 6-25 cm. long. 16. O. ursina. 



Fruits fleshy and juicy when mature, bearing glochids but not appreciably spiny. 



Plants large shrubs or arborescent, 1.5-5 m. tall, with a well-defined trunk and ascending branches. 

 Joints 2-5 dm. long; trunk spineless; fruit 5-9 cm. long; spines brown or white. 



Fruit yellow to reddish yellow; umbilicus flat; spines brownish. 17. O. megacantha. 



Fruit deep red to purplish; umbilicus depressed; spines white. 18. O. ficus-indica. 



Joints 0.75-2 dm. long; trunk densely clothed with deflexed spines; fruit 3-5 cm. long; 

 spines yellow. 19. O. chlorotica. 



Plants low shrubs or assurgent, much branched from the base, usually less than 1 m. high. 



Spines clear yellow, or faintly reddish at the base, curved downward or deflexed in age; 



coastal. 20. O. littoralis. 



Spines white, reddish or brown, spreading. 



Flowers salmon to magenta; joints usually less than 20 cm. long, not very spiny; spines 

 1-3 per areole or lacking, not over 3 cm. long. 21. O. Vaseyi. 



Flowers yellow; joints frequently much more than 20 cm. long, spiny; spines 1-6 cm. 

 long. 



Joints ovoid to oblong, 1.5-3 times as long as broad. 22. O. Covillei. 



Joints broadly ovoid to orbicular, usually as broad as long, or nearly so. 



Plants low bushes; branches few to many joints high; spines brownish only at 

 the base. 

 Spines 3-8; joints comparatively thick; cismontane. 23. O. occidentalis. 



Spines mostly 1-2 (1-4); joints comparatively thin; western margin of 

 deserts. 24. O. megacarpa. 



Plants prostrate, branches forming chains of joints, on edge, mostly 2 joints 

 high; spines predominantly brownish throughout; eastern Mojave Desert. 



25. O. mojavensis. 



