EVOLUTIONARY TRANSITIONS BETWEEN STATES OF STRUCTURAL AND DEVELOPMENTAL CHARACTERS AMONG THE ALGAL CHAROPHYTA (VIRIDIPLANTAE)

Abstract

The Charophyta comprise green plant representatives ranging from familiar complex-bodied land plants to subtle and simple forms of green algae, presumably the closest phylogenetic relatives of land plants. This biological lineage provides a unique opportunity to investigate evolutionary transition series that likely facilitated once-aquatic green plants to colonize and diversify in terrestrial environments. A literature review summarizes fundamental structural and developmental transitions observed among the major lineages of algal Charophyta. A phylogenetic framework independent of morphological and ontological data is necessary for testing hypotheses about the evolution of structure and development. Thus, to further elucidate the branching order of the algal Charophyta, new DNA sequence data are used to test conflicting hypotheses regarding the phylogenetic placement of several enigmatic taxa, including the algal charophyte genera <i>Mesostigma</i>, <i>Chlorokybus</i>, <i>Coleochaete</i>, and <i>Chaetosphaeridium</i>. Additionally, technical notes on developing RNA methods for use in studying algal Charophyta are included.