THE GENUS PELECYPHORA (CACTACEAE): RESOLUTION OF A CONTROVERSY

The four species considered in this article fall into two natural groups. The evidence presented for this conclusion involves not only external features such as floral, fruit, and seed morphology, but also that obtained from internal structure, including tubercle and areole development, the anatomy of surface layers of mature tubercles, the structure of crystals in the ground tissues, and features of tracheary elements. When all evidence is considered, it becomes apparent that Pelecyphora aselliformis and Encephalocarpus strobiliformis are cogeneric as are P. valdeziana and P. pseudopectinata. Yet, the two cogeneric pairs are not closely related to each other. We do not propose to place them in any phylogenetic scheme as yet because general knowledge of the family Cactaceae is still too fragmentary. The first pair is assigned to Pelecyphora, of which a formal taxonomic treatment is presented, and the second pair is tentatively assigned to Thelocaclus.