The genus Ceratozamia comprises about 16 species with restricted distribution north and south of the Eje Neovolcanico in Mexico. Phylogenetic relationships were explored among species of Ceratozamia, using 24 exemplars and seven putative outgroup taxa. We examined variation at the molecular level in two non-coding regions from the chloroplast and nuclear genomes. Although the rate of change of the ITS and trnL-F non-coding regions is considered appropriate to recover variation at this taxonomic level, only 33 nucleotide positions were informative out of 2081. Despite low levels of variation, analyses showed that Ceratozamia is monophyletic and identified Zamia as sister group. The molecular phylogeny of Ceratozamia revealed three main clades, which allow for biogeographic interpretations. The most basal clade suggests a probable ancestral geographic area for Ceratozamia in Southeast Mexico. Another implication is that speciation within the genus appears to be associated with the post-Pleistocene spread of floristic communities from proposed Pleistocene tropical refugia located in S. E. Mexico towards north of the Eje Neovolcanico.

Communicating Editor: Thomas G. Lammers