Format: ORAL

Susana Magalln1, Adriana Bentez-Villaseor2, Laura Calvillo-Canadell1, Csar A. Gonzlez-Martnez2, Andrea M. Lpez-Martnez2, Eduardo Torres-Flores2, Karina Yez-Aroche2

1 Institute of Biology, Universidad Nacional Autónoma de México, Mexico City, Mexico 2 Graduate Program in Biological Sciences, Universidad Nacional Autónoma de México, Mexico City, Mexico

Seed plants diversified profusely during the Paleozoic, giving rise to most of their major lineages, and a vast morphological and functional diversity. Reconstructing seed plant relationships has been a major challenge due to a deep conflict between morphological and molecular phylogenies. Here, we review some major challenges, summarize what has been learned, and propose potential ways forward. Representative sampling is a major obstacle because the number of extinct lineages vastly surpasses the five extant branches, and includes those derived from the earliest radiation of the group; extinct crown group lineages; and stem members of extant branches, which may hold clues to understanding relationships. The nature of plants typically results in fragmentary preservation and missing data. Recognition of the need to strive for whole plant reconstructions and to include species as terminals are important advances. Molecular phylogenetic estimation is complicated because extant species represent recent branches within lineages that diverged in the deep past. Molecular data has been shown to be systematically biased, and genomic datasets have not improved resolution. Paleobotanical discoveries and revised interpretations of fossil characters can critically improve phylogenetic estimation. Inconsistent taxon representation among different data sets precludes direct comparison of estimated relationships. Furthermore, different interpretations of primary homology, of structural attributes of particular fossils, and scoring philosophy result in phylogenetic lability. Analyses combining morphological and molecular data under model-based phylogenetic methods have been insufficiently exploited in the estimation of seed plant relationships, and implementation of novel approaches to model morphological character substitution hold promise. The Fossilized Birth-Death model, which integrates fossils and extant species into a single diversification process, may represent a potential alternative. Nevertheless, placement of fossils ultimately relies on morphological data, hence rigorous character assessment based on meticulous observations and thoughtful postulations of primary homology is inescapable.