Cryptic diversity, sympatry, and other integrative taxonomy scenarios in the Mexican Ceratozamia miqueliana complex (Zamiaceae)

According to the integrative taxonomy (IT) framework, delimitation of taxonomic specimens into bona fide species requires the incorporation of multiple sources of biological evidence that jointly perform a role as systematic criteria. Here, we collected a combination of geographic, morphological (qualitative and quantitative), and molecular data sets from a group of specimens in the Ceratozamia miqueliana species complex. We analyzed them under methods suitable for each of these partitions and then synthesized results under the taxonomic circle-i.e., an operational tool for inference in IT. Taxonomic circle-based species delimitations in this Ceratozamia species complex have downstream taxonomic-nomenclatural consequences given that morphometric affinity between these specimens does not allow their species-level identification. However, joint patterns of qualitative morphological (i.e., diagnostics in standard sense) and molecular (i.e., character-based, DNA diagnostic or "bar coding") characters between the species suggest the following scenarios: (1) C. miqueliana is a morphologically diagnosable species that lacks DNA diagnostics; (2) Ceratozamia subroseophylla is diagnosable both in terms of morphological and molecular evidence and sympatric with C. miqueliana; (3) Ceratozamia euryphyllidia is diagnosable both in morphological and molecular terms; (4) Ceratozamia zoquorum and Ceratozamia santillanii are cryptic species, i.e., both have exclusive DNA diagnostics but are not diagnosable morphologically; and (5) Ceratozamia becerrae is not diagnosable by any criterion and should therefore fall in synonymy. The present work contributes to establish a robust platform for subsequent systematic assessments of Mexican cycad diversity, which could include new hypotheses on the evolutionary processes involved in their current biogeographic distribution, ecological relationships, and other life-history aspects, in turn useful for conservation biology concerns.