6 THE CACTACEAE. 



2. THELOCACTUS (Schumann) Britton and Rose, Bull. Torr. Club 49: 251. 1922. 



Cacti of medium size, globular or somewhat depressed, spi^3^ often densely so; ribs few, low 

 or even indefinite, di\nded into large, often spiraled, tubercles; flowering tubercles more or less 

 grooved above; flowers from near center of plant, borne on very j'oung tubercles, rather large for 

 the subtribe, campanulate, diurnal; scales on ovary usually few, their axils naked; fruit so far as 

 known dn.^ dehiscing by a basal pore; seeds black, finely tuberculate, with a large basal hilum. 



Type species : Echinocactits liexaedrophorus Lemaire. 



The generic name is from d-qXri nipple, and cactus, referring to the tubercled ribs. 

 Thelocactiis was used for a subgenus of Echinocachis by Schumann; he described it with 

 "ribs mostly divided into spirally disposed tubercles or mamillae, not protruding like a 

 chin at base; spines straight or slightly curved." He referred to the group a number of 

 diverse species representing several generic types, some of which we took up in Volume III. 



We recognize 12 species, all native of Mexico. 



To this genus we have referred the Echinocacti of previous authors which seem to 

 intergrade with the Coryphanthanae. The group is perhaps complex and may contain 

 two or more distinct genera, but most of the species are little known. 



Key to Species. 



Ribs indefinite, strongly tubercled. 

 Spines all straight. 



Tubercles not flattened laterally; radial spines 6 to 9 i . T. liexaedrophorus 



Tubercles flattened laterally; spines i to 5. 



Flowers white 2 . T. rinconensis 



Flowers not white. 



Flowers salmon to j'ellow 3. T. lophotliele 



Flowers rose-purple 4. T. phymatothele 



Some of spines cur\-ed outward 5 . T. biiekii 



Ribs definite, but more or less divided into tubercles. 

 Flowers yellowish. 



Ribs 8 to 13 6. T. leucacaiitlius 



Ribs 20 to 25 , 7. T. nidulans 



Flowers red to purple. 

 Spines all straight. 



Spines subulate 8. T. fossulatus 



Spines acicular ; 9. T. Iiilensis 



Spines more or less cur\-ed. 



Spines 8 or fewer 10. T. Uoydii 



Spines numerous. 



Central spines flexible, usually straight, porrect or ascending ii. T. bicolor 



Central spines subulate, rigid, some of them curved and reflexed 12. T. pottsii 



1. Thelocactus hexaedrophorus (Lemaire) Britton and Rose, Bull. Torr. Club 49: 251. 1922. 



Echinocaclus hexaedrophorus Lemaire, Cact. Gen. Nov. Sp. 27. 1839. 

 Echinocactits hexaedrophorus roseus Lemaire in Labouret, Monogr. Cact. 251. 1853. 

 Echinocaclus hexaedrophorus labouretianus Schumann, Gesamtb. Kakteen 438. 1898. 

 Echinocaclus hexaedrophorus major Quehl in Schumann, Gesamtb. Kakteen 438. 1898. 



Globose or somewhat flattened above or umbilicate, glaucous, strongly tubercled, 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 

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

 stigma-lobes yellov^nsh white. 



Type locality: Tampico, Alexico. 



Distribution: Central Mexico. 



Schumann refers a plant from San Luis Potosi* to this species. The type, however, 

 is said to have come from Tampico on the coast, while San Luis Potosi is on the table-land at 

 an altitude of 7,000 feet or more, and such an altitudinal distribution is not to be expected. 

 It is possible, but hardly probable, that the plant was actually collected at San Luis Potosi 

 but shipped from Tampico, the port of San Luis Potosi, as such mistakes were common 

 in the early shipments of cacti. Thus, species are attributed to Buenos Aires which came 



* This plant of the table-land is Echinocaclus fossulalus Scheidweiler. 



