OPUNTIACEAE. 815 



white above, about 5 cm. long : fruit scarlet, subglobose, 16-18 mm. in diameter : seeds reni- 

 form, 2.4-2.8 mm. long, black, smooth and shining or minutely pitted. 

 On prairies, south-central Texas and adjacent Mexico. 



4. Echinocactus Wrightii (Engelm.) Small. Stems ovoid or oval, 7.5-15 cm. 

 high, 5-8.5 cm. thick, the ribs 13, with interrupting tubercles grooved to the base : spines 

 various ; radials about 8, 3-5 cm. long, the upper straight, flattened, the 3 lower hooked, 

 terete, darker than the upper ; central solitary, 5-15 cm. long, erect, straw-colored with a 

 dark tip, zigzag, hooked : flowers dark purple, 2.5-3.5 cm. long: fruit reddish, 1.5-2.5 

 cm. long, fleshy : seeds flattened, curved, 1.4-1.6 mm. long, tuberculate, keeled along the 

 back. [E. uncinatus var.? Wrightii Engelm.] 



In dry soil, along the Rio Grande, Texas and adjacent Mexico. 



5. Echinocactus Muhlenpfordtii Fen. Stems globose-ovoid to oblong-cylindric, 10- 

 20 cm. high, the ribs often 13, more or less oblique : spines various ; radials 10-12, subu- 

 late, bristle-like, 12-32 mm. long, the upper longer than the lower ; central solitary, firm, 

 25-35 mm. long, hooked : flowers 5-7 cm. long, yellow and scarlet within : fruit globular, 

 red, 8-10 mm. long. 



In sandy soil, Texas and adjacent Mexico. 



5. OPUNTIA Mi 



Fleshy plants, with conspicuously jointed stems, the joints flat or terete. Leaves scale- 

 like, caducous, spirally arranged. Areolae axillary, usually spine-bearing. Flowers lateral, 

 arising from the cushions of remote bristles of the areolae. Hypanthiun bearing areolae, 

 not prolonged beyond the ovary. Sepals spreading, in several rows. Petals forming a rotate 

 corolla. Ovary 1-celled : style cylindric : stigma 5-8-lobed. Berry more or less pear- 

 shaped, fleshy or sometimes dry. Seeds flattened or disk-like. Embryo curved around 

 the endosperm. PRICKLY PEAR. 



Joints flat. 



Spines wanting. 1. 0. Ficus-Indica. 



Spines present, sometimes deciduous. 

 Fruit fleshy. 



Spines flattened. 

 Stems erect. 



Plants usually less than 12 dm. tall : flowers mostly over 7.5 cm. 



broad. 2. 0. Tuna. 



Plants usually over 12 dm. tall : flowers mostly less than 7.5 cm. 



broad. 3. 0. Engelmannii. 



Stems procumbent. 4. O. tortispina. 



Spines terete or nearly so, sometimes barely angled. 

 Flowers over 5 cm. broad. 



Joints mainly over 12 cm. long : flowers over 11 cm. long. 5. 0. grandiftora. 



Joints mainly less than 12 cm. long : flowers less than 9 cm. long. 

 Roots fusiform or tuberous. 



Joints narrowly obovateor oblong-obovate : species campes- 



trian. 6. 0. macrorhiza. 



Joints broadly obovate or orbicular-obovate : species Floridian. 7. O. austrina. 

 Roots fibrous. 



Spines white tinged at the ends. 8. 0. humifusa. 



Spines brownish black. 9. 0. fusco-atra. 



Flowers less than 5 cm. broad. 



Spines less than 2.5 cm. long : joints about twice as long aswide, or 



less. 10. 0. Opuntia. 



Spines over 2.5 cm. long : joints many times as long as thick. 11. O. Pes-Corvi. 



Fruit dry. 12. 0. polyacantha. 



Joints terete, slender. 13. 0. leptocaulis. 



1. Opuntia Ficus-Indica (L.) Mill. Stems erect, 12-18 dm. tall, proliferous : trunk 

 cylindric, woody in age, the joints thick, obovate to elliptic, 10-15 cm. long, with the 

 cushions of bristles immersed, spineless or sometimes with a very short spine : flowers 

 yellow, 7.5-10 cm. broad : fruit obovoid, bristly, 5-6 cm. long, edible, the pulp red. 



In sand, peninsular Florida and the West Indies. 



2. Opuntia Tuna (L. ) Mill. Stems erect, 9-12 dm. tall, proliferous, the joints oval 

 or elliptic, 10-20 cm. long : cushions or bristles remote above, a cluster of 4-6 short rigid or 

 subulate yellow spines, varying from very short to 3.5 cm. in length : flowers yellow or red- 

 dish yellow, 7.5-10 cm. broad : fruit rather pear-shaped, 5-6 cm. long, edible. 



In sandy soil, peninsular Florida, the West Indies and Central America. 



3. Opuntia Engelmannii Salm-Dyck. Stems erect, 12-18 dm. tall, forming a woody 

 trunk, sometimes 15 cm. thick and clothed with a grayish bark, the joints pale green, 

 obovate or orbicular-obovate, becoming 30 cm. long and sometimes 22 cm. broad ; cushions 

 of bristles remote : spines few, 2.5-3.5 cm. long, or some shorter, flattened or angled, straw- 



