6 THE CACTACEAE. 
a 
AY 3) 2. THELOCACTUS (Schumann) Britton and Rose, Bull. Torr. Club 49: 251. 1922. 
a Cacti of medium size, globular or somewhat depressed, spiny, often densely so; ribs few, low 
or even indefinite, divided into large, often spiraled, tubercles; flowering tubercles more or less 
grooved above; flowers from near center of plant, borne on very young tubercles, rather large for 
the subtribe, campanulate, diurnal; scales on ovary usually few, their axils naked; fruit so far as 
known dry, dehiscing by a basal pore; seeds black, finely tuberculate, with a large basal hilum. 
Type species: Echinocactus hexaedrophorus Lemaire. 
The generic name is from 677 nipple, and cactus, referring to the tubercled ribs. 
Thelocactus was used for a subgenus of Echinocactus 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 0 1. 7. hexaedrophorus 
Tubercles flattened laterally; spines 1 to 5. 
Flowers white 
Flowers not white. 
Flowers salmon to yellow. ........00 0000 e cece cece cccucccuccceeeee. 3. T. lophothele 
; Flowers rose-purple..........0..000.0 00. e cece cece eee cece lel. 4. T. phymatothele 
Some of spines curved outward........0.0.0.0.0 0 0c cece cee eee 5. I. buekii 
cee eee eee eet e eb ee ee eaeceeseees 2. T. rinconensts 
Ce 6. T. leucacanthus 
oP ee cea Segoe ERS ete tee eaten tee nent esate eenseeeees 7. T. nidulans 
Spines all straight. 
Spines subulate 
i DUAL cece eee eee ene en beenees 8. T. fossulatus 
Spines acicular 
, PPIMES ACICULAT. 0. eee eee cece tent ac ev ececeecees g. T. tulensts 
Spines more or less curved. 
Spines 8 or fewer... 0c ete ccc cece cee cccec ccc cee. 10. 7. lloydit 
Spines numerous. 
Central spines flexible, usually straight, porrect or ascending........... 11. JT. bicolor 
Central spines subulate, rigid, some of them curved and reflexed........ 12. T. pottsi 
V1. Thelocactus hexaedrophorus (Lemaire) Britton and Rose, Bull. Torr. Club 49: 251. 1922. 
7”, Echinocactus hexaedrophorus Lemaire, Cact. Gen. Nov. Sp. 27. 1839. 
Echinocactus hexaedrophorus roseus Lemaire in Labouret, Monogr. Cact. 251. 1853. 
Echinocactus hexaedrophorus labouretianus Schumann, Gesamtb. Kakteen 438. 1898. 
Echinocactus 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 
arge, 5.5 cm. long and broader than long when expanded; perianth-segments oblong, purplish; 
stigma-lobes yellowish white. 
Type locality: Tampico, Mexico. 
Distribution: Central Mexico. ~ 
_ Schumann refers a plant from San Luis Potosi* 
is said to have come from Tampico on the coast, while 
an altitude of 7,000 feet or more, and such an altitudi 
It is possible, but hardly probable, that the plant wa 
but shipped from Tampico, the port of San Luis P 
in the early shipments of cacti. 
to this species. The type, however, 
San Luis Potosi is on the table-land at 
nal distribution is not to be expected. 
s actually collected at San Luis Potosi 
otosi, as such mistakes were common 
Thus, species are attributed to Buenos Aires which came 
* This plant of the table-land is Echinocactus fossulatus Scheidweiler. 
