STANDLEY TREES AND SHRUBS OF MEXICO. 877 



Stems low, usually less than 30 cm. high, much branched, creeping, form- 

 ing broad impenetrable masses 2 to 3 meters in diameter ; joints 10 to 15 

 cm. long, clavate, more or less curved, strongly tuberculate; tubercles 3 

 to 4 cm. long, flattened laterally, 4 to 6 cm. apart ; spines numerous, stout, 

 elongate, somewhat roughened, reddish brown, the larger ones strongly flat- 

 tened, 8.5 to 6 cm. long ; flowers yellow, 5 to 6 cm. broad ; fruit ovate, 

 clavate at base, yellow, 5 to G cm. long, very spiny, with a depressed um- 

 bilicus ; seeds flattened, 4.5 to 6.5 mm. in diameter. 



27. Opuntia schottii Engelm. Proc. Amer. Acad. 3: 304. 1S58. 

 Northern Mexico. Texas. 



Prostrate, rooting from the areoles, forming dense clusters sometimes 2 

 or 3 meters in diameter; joints clavate, curved, ascending, easily breaking 

 off, 6 to 7 cm. long, 2 cm. in diameter at thickest part, strongly tuberculate ; 

 areoles 1 to 1.5 cm. apart ; spines white and sheathed when young, soon 

 brown, the larger ones sometimes as many as 12, very slender, sometimes 

 6 cm. long, somewhat flattened ; wool white when young, turning brown ; 

 glochids white when young, turning brown, 4 mm. long or less; flowers 

 yellow, 4 cm. long (including ovary) ; sepals narrow, acuminate; petals 

 acuminate; fruit yellow, narrowly oblong, a little narrowed at base, 4 cm. 

 long, closely set with areoles bearing numerous short spines, bristles, and 

 white wool, the umbilicus depressed ; seeds yellow, flattened, 4 mm. in diameter, 

 notched at base. 



28. Opuntia vilis Rose, Contr. U. S. Nat. Herb. 12: 293. 1909. 

 Zacatecas. 



Low, creeping, often forming mats several meters in diameter and only 10 to 

 Vu cm. high ; joints prostrate, becoming erect or ascending, the ultimate verti- 

 cal ones clavate, 5 cm. long, the others 2 to 4 cm. long, very turgid, pale green, 

 with low tubercles ; young areoles bearing white wool ; radial spines upward 

 of 12, the number increasing with age by the addition of very small whitish 

 ones ; central spines on prostrate joints 4, reddish, white-tipped, 1 to 4 cm. 

 long, terete, slightly scabrous, with a sheath 5 mm. long, those of clavate joints 

 white, reddish on the upper surface at base ; flower 4 cm. long ; petals brilliant 

 purplish, 2 cm. long; fruit pale green, 2 to 2.5 cm. in diameter, 2.5 to 3 cm. 

 long, tuberculate, especially about the margin of the umbilicus, spiny, some- 

 what dry, with large white seeds. 



29. Opuntia bulbispina Engelm. Proc. Amer. Acad. 3: 304. 1856. 

 Coahuila and Durango ; type from Perros Bravos, north of Saltillo. 



Stems low, forming wide-spreading clumps 0.6 to 1.2 meters broad ; joints 

 cvoid, 2 to 2.5 cm. long, 10 to 12 mm. in diameter ; tubercles prominent, 6 to 8 

 mm. long; radial spines 8 to 12, acicular, 3 to 6 mm. long; central spines 4, 

 much stouter than the radials, 8 to 12 mm. long, bulbose at base; flower and 

 fruit unknown. 



30. Opuntia grahamii Engelm. Proc. Amer. Acad. 3: 304. 1856. 

 Chihuahua. Texas and New Mexico ; type from El Paso. 



Roots at flrst thick and fleshy, becoming woody, 2 cm. thick or more; plants 

 low, much branched, spreading, forming low mounds often half buried in sand, 

 sometimes giving off roots at the areoles ; terminal joints erect, clavate, bright 

 green, 3 to 5 cm. long, with large oblong tubercles ; areoles about 3 mm. broad ; 

 wool white ; spines 8 to 15, slender, slightly scabrous, terete or some of the 

 larger ones slightly compressed, white when young, soon reddish, the longest 3.5 



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