Species delimitation in Ceratozamia (Zamiaceae) from Southwestern Mexico, in light of reproductive and climatic diversification

Multidisciplinary taxonomic studies have enhanced the delimitation of species within complex taxonomic groups. In the cycad genus Ceratozamia , the taxonomy is still not fully resolved for the several species complexes that have been proposed. Five Ceratozamia species occur in geographic proximity in the Soconusco region of southwestern Mexico. Because of similarity and variable morphology across these species, their taxonomy is a source of confusion. Based on integrative taxonomy, including morphological (qualitative and quantitative), ecological, and molecular data, we aimed to diagnose the species from the Soconusco region. We carried out extensive field sampling, collecting 225 individuals from a total of 12 populations, and reviewed one hundred herbarium specimens to evaluate whether the species are diagnosable. We carried out morphometric analyses at the population level on vegetative and reproductive characters and present the first analyses of phenotypic variability of pollen and ovulate strobili in neotropical cycads. Additionally, we evaluated the influence of climatic factors on morphological variation. Morphological characters of ovulate strobili were correlated with climatic conditions. In contrast, there was no significant correlation between the morphology of pollen strobili and the environment. In the pollen strobili, we found fixed characters that allow for the identification of the species. The haplotype networks displayed several groups of related haplotypes, which in some species corresponded to mixed population clusters. We detected a discordance between phenotypic and genetic evidence. The integration of evidence offers grounded views for clarifying species boundaries and outlining the differences among species, which we incorporated into a taxonomic key. In general, the mixed relations within this group of species may be due to historical hybridization events favored by common phenology and sharing of biotic pollination vectors. Finally, based on our results, we discuss the use of morphology for species delimitation and inference of evolutionary relationships in cycads.