ulvophytes are often not resolved as monophyletic with molecular data. Many of the taxa currently included in Trebouxiophyceae would not have been placed in this class on the basis of morphology alone. Two other classes based upon ultrastructure (Prasinophyceae, Charophyceae) are grades that should be reclassified. Another important impact of molecular data has been resolution of relationships among the problematic coccoid green algae (especially of the strictly autosporic taxa without swimming cells). No doubt there will be many more profound changes to come in the classification of these groups. Molecular data are also expanding our view of diversity, both in familiar taxa and in newly revealed, previously unsampled taxa. The distinct lineages of paraphyletic Chlamydomonas were not distinguished because they possess nearly identical flagellar structure. Culture-based or "environmental sampling" studies that include molecular data have documented novel lineages (Phillips and Fawley, 2000 ? ; Lewis and Flechtner, 2003) that are now being characterized. If these new taxa correspond to critical or early diverging lineages, their inclusion in future analyses could have a profound impact on our understanding of relationships among the major groups of green algae. Despite these advances, molecular data thus far have failed to resolve firmly some of the deeper branches of the green plant tree of life, including the monophyly of the ulvophyte algae, the relationships among lineages in the Chlorophyceae, and the topology of the prasinophyte algae. A contributing factor to this lack of resolution is a paucity of data compared to that from other plant