Abstract
Cycads have the oldest fossil record among extant spermatophytes (seed plants). However, their ‘living fossils’ status has been recently questioned, based on the results of molecular phylogenetic studies. The group has morphological apomorphies, mainly in vegetative but possibly also in reproductive characters, with Cycas as the most divergent genus. Besides Australia and South Africa, Mexico is one of the 3 centers of diversity for the order Cycadales, with 54 species belonging to 3 of the genera comprising the family Zamiaceae: Ceratozamia, Dioon and Zamia. The percentage of the Mexican species of Zamiaceae (88.9%) represents the highest value for this parameter for the family in the Neotropics. Overall, the state of conservation for the 3 genera is critical, since all Mexican cycad species are included in a risk category, according to the Nom-059-Semarnat-2010. Finally, we consider that the knowledge generated so far on Mexican cycads, in terms of systematics, evolutionary and conservation biology, will allow us to clarify different evolutionary scenarios, especially those related to the processes and patterns that have shaped its current diversity.
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