Ceratozamia gigantea (Zamiaceae), a new species of cycad, endemic to the mountain karst forests of Tabasco, Mexico: what the reproductive structures revealed.

Summary: Ceratozamia is a diverse genus of cycads distributed from Mexico to Honduras. Here, a new species of Ceratozamia (Zamiaceae, Cycadales) from the southeast of Mexico is described and illustrated. It was previously misidentified as C. subroseophylla because of the lack of reproductive structures in the specimens from Tabasco. This work is based on phenological monitoring carried out in a karst limestone locality in Tabasco. The lifespan of pollen and ovulate strobili and their morphological changes throughout development are described. The collections of this new species were compared with specimens of all Ceratozamia species; however, the morphological comparison was focused on the most geographically proximate and morphologically similar species to this new taxon. To evaluate the circumscription of this species, we used geographic, morphological and DNA barcoding criteria. On this basis, we propose a new species of Ceratozamia for Mexico and provide notes on its reproductive phenology. The reproductive structures are the primary resource for its recognition and identification. A taxonomic key for the similar morphological species and all species that occur in Tabasco is presented along with habitat characterisation and a conservation status for C. gigantea. This species, whose distribution is restricted to a small geographic area, increases the diversity of Ceratozamia in Tabasco to three species and affirms the importance of limestone karst as areas for speciation and endemism. During the phenological monitoring, pollinator insects were captured on ovulate strobili at receptivity, observations that have been scarcely documented during this phenophase in Ceratozamia, highlighting the relevance of monitoring reproductive phenological patterns. [ABSTRACT FROM AUTHOR]