Photosynthetic green plants, the Viridiplantae, are composed of two distinct lineages, the Chlorophyta and Charophyta. The Chlorophyta include the Chlorophyceae, Trebouxiophyceae, Ulvophyceae and most prasinophytes. The Charophyta include the Mesostigmatales, the traditional charophycean green algal orders Chlorokybales, Klebsormidiales, Zygnematales, Coleochaetales and Charales, and land plants, referred to here as Embryophyceae. The Embryophyceae are embedded within the paraphyletic charophycean green algae, so land plants are therefore best considered a specialized group of green algae adapted to terrestrial life. Due to the close evolutionary relationship between green algae and Embryophyceae, characterizing the early evolution and diversification of land plants depends on understanding phylogenetic relationships among the less extensively studied green algal members of the Charophyta. Relationships within the Charophyta have previously been based on morphology and inferred through phylogenetic analyses of molecular data that include ribosomal DNA and several genes from the chloroplast and mitochondrial genomes. To this point, however, few phylogenetic analyses of nuclear, protein-coding genes have been conducted. We are attempting to isolate and sequence actin-coding regions from representative members of the Charophyta. Actin is a highly conserved protein that is ubiquitous among eukaryotes; these features make actin an ideal subject for comparative sequence analysis. A major component of the cytoskeleton, actin plays a number of important roles in plant cell processes such as cell division and cytoplasmic streaming. Hence, in addition to being potentially useful for resolving organismal relationships, the evolution of the actin protein itself is intrinsic to the study of morphological evolution and development within green plants.

Key words: actin, Charophyta, evolution, green algae, phylogeny