[Zimmerman A. D., Parfitt B. D., Echinocactus, Flora of North America North of Mexico. Volume 4: Magnoliophyta: Caryophyllidae, part 1, Oxford University Press, New York and Oxford, 2003a, tom 4, s. 188–191]
A floristic treatment of North American species under the name Echinocactus. It contains descriptions of stems, spines, flowers, fruits and seeds, a key and habitat data. The descriptions of E. polycephalus and E. texensis that were read concern species now placed in Homalocephala by POWO.