The powerful new tool of comparing molecules to show evolutionary relationships will be used in studying freshwater and marine green algae, including those green algae thought to be most closely related to the land plants. A comparison of the ribonucleic acid (RNA) molecules from cytoplasmic ribosomes will offer a new and exciting perspective on questions that have been the focus of research attention for more than a century. Other modern approaches, such as electron microscopy, have provided major revisions of the classification of green algae, revisions that can now be tested by molecular analysis. The comparison of cytoplasmic ribosomal RNA molecules of green algae also will provide a major basis for comparison to similar studies of the molecular evolution of the chloroplasts of green algae, an evolution that may be different from that of the cytoplasmic ribosomal RNAs. Also, this study will be a model for and parallel to studies of other major groups of algae including red and brown algae, the diatoms, and the dinoflagellates. In this project portions of the 18s and 26s ribosomal RNA molecules will be sequenced directly (by dideoxynucleotide primer extension). The massive data set will be stored, aligned, compared, and analyzed with various computer programs. Cladistic analysis of the data will provide the basis for inferring the ancient lineages and patterns of divergences for the green algae. The "family trees" produced will be contrasted with those based on morphological, ultrastructural, and biochemical characters. Computer-assisted cladistic analysis of ribosomal RNA data in combination with non-molecular information will provide an important synthesis of different types of information and thus, should help us develop a natural system of classification for the green algae and a better understanding of the algal origins of land plants.
