Molecular Systematics of the Green Algae

Ranging from unicells to complex “plantlike” organisms that are adapted to habitats from subaerial or terrestrial to freshwater or marine, the green algae represent a diversity of life forms that offer a daunting challenge in the search for shared morphological characters. The ultrastuctural techniques that fueled the 1970s and early 1980s revolution in algal systematics revealed a suite of new morphological characters, but many were not global (i.e., present in all of the taxa). Controversy over the interpretation of the importance of ultrastructural features (e.g., of cell division versus flagellar apparatus) led to conflicting hypotheses. Also, different researchers studied different details of different taxa, and thus a data matrix reporting a complete set of morphological and ultrastructural characters over a wide range of algal taxa was not available. Thus, it is no wonder that many researchers interested in unraveling the mystery of green algal phylogeny embraced molecular systematics, hoping that its early promise of relatively simple access to ample global characters would lead, finally, to a “true” phylogeny. The extent to which this promise has been fulfilled, or is likely to be fulfilled, is the subject of this chapter.