Phylogenetic relationships among ferns and gymnosperms; an overview

Abstract

Ferns and gymnosperms are two of the most important traditionally recognized groups of vascular plants, but both are unnatural when viewed in terms of phylogenetic systematics. That is to say that neither consists of a monophyletic group. Nevertheless, both continue to be recognized as informal groupings of plants because representatives of each have similar grades of structural and reproductive features, and because many aspects of their natural relationships remain equivocal. Monophylesis for some traditionally recognized groups of pteridophytes and gymnosperms is fairly well established, but is unresolved or highly suspect for others. The latter include fernssensu lato, filicalean ferns, seed ferns and coniferophytes. Some recent studies also question whether conifers represent an unnatural assemblage. However, a taxon that includes the Marsileales and Salviniales recently has been interpreted to be monophyletic. Comparisons of results from phylogenetic analyses using either morphological or molecular characters provide a basis for assessing the strengths of systematic hypotheses and suggest fruitful avenues for future study. It is clear from all approaches that the greatest impediment to resolution of phylogenetic relationships in the inadequate rate at which new data are being developed.