STANDLEY TEEES AND SHRUBS OF MEXICO. 957 



Ribs definite, but more or less divided into tubercles. 

 Flowers yellowish. 



Ribs 8 to 13 6. T. leucacanthus. 



Ribs 20 to 25 7. T. nidulans. 



Flowers red to purple. 

 Spines all straight. 



Spines subulate 8. T. fossulatus. 



Spines acicular 9. T. tulensis. 



Spines more or less curved. 



Spines 8 or fewer 10. T, lloydii. 



Spines numerous. 

 Central spines flexible, usually straight, porrect or ascending. 



11. T. bicolor. 

 Central spines subulate, rigid, some of them curved and reflexed. 



12. T, pottsii. 



1. Thelocactus hexaedrophonis (Lemaire) Britt. & Rose, Bull. Torrey Club 



49: 251. 1922. 



Echinocactus hexaedrophorus Lem. Cact. Hort. Monv. 27. 1839. 



Central Mexico ; tj'pe from Tampico, Tamaulipas. 



Globose or somewhat flattened above or umbilieate, glaucous, strongly tuber- 

 cled, not ribbed, 13 to 14 cm. in diameter ; tubercles prominent, somewhat 

 6-sided, 27 mm. broad at base, arranged in indefinite spirals ; radial spines 6 

 to 9, spreading, unequal, 11 to 18 mm. long, rigid, straight, subulate, annulate; 

 central spine much stouter than the radials, erect, 2.3 to 3 cm. long; flowers 

 5.5 cm. long and broader than long when expanded ; perianth segments oblong, 

 purplish. 



2. Thelocactus rinconensis (Poselger) Britt. & Rose, Cactaceae 4: 7. 1923. 

 Echinocactus rinconensis Poselger, Allg. Gartenz. 23: 18. 1855. 



Nuevo Le6n ; type from Rinconada. 



Simple, globose or somewhat depressed, 6 to 8 cm. high, 12 cm. in diameter ; 

 ribs somewhat spiraled, strongly tubercled; tubercles more or less flattened 

 laterally, somewhat angled ; spines usually only 3, acicular, 1.5 cm. long ; 

 flowers white, 4 cm. long; inner perianth segments lanceolate, acute. 



3. Thelocactus lophothele (Salm-Dyck) Britt. & Rose, Bull. Torrey Club 49: 



251. 1922. 



Echinocactus lophothele Salm-Dyck, Allg. Gartenz. 18: 395. 1850. 



Chihuahua ; type from Chihuahua City. 



Simple or in its native state cespitose, globose, sometimes depressed or 

 short-cylindric, up to 25 cm. high, glaucous; ribs indefinite, strongly tubercu- 

 late, the tubercles flattened; areoles depressed, grayish-lanate when young; 

 radial spines 3 to 5, stout, purplish brown, 1 to 3 cm. long; central spines 

 wanting or solitary ; flowers salmon to rose, about 5 cm. broad ; perianth seg- 

 ments nearly linear, acute ; scales of ovary glabrous, 6 mm. long. 



4. Thelocactus phymatothele (Poselger) Britt. & Rose, Cactaceae 4: 8. 1923. 

 Echinocactus phymatothelos Poselger; Forst. Handb. Cact. ed. 2. 602. 1885. 

 Mexico, the range not known. 



Simple, depressed-globose, 5 cm. high, 9 to 10 cm. in diameter ; ribs glaucous- 

 green, 13, divided into low irregular tubercles, these somewhat flattened and 

 pointed ; spines usually 1 to 3, sometimes wanting, subulate, rigid, 2 cm. long, 

 brown, spreading ; flowers 6 cm. broad ; inner perianth segments pinkish, 

 narrow, acute ; scales present on ovary and flower tube. 



