Macroalgal Phylogeny

Abstract

The term ‘algae’ is a traditional and colloquial term used to denote the microscopic to macroscopic photosynthetic organisms most commonly studied by phycologists. The macroscopic marine algae that are the focus of this chapter are commonly known as the green, red and brown seaweeds. Despite the pejorative connotation of the term ‘seaweed’, these photosynthetic organisms are of major positive importance worldwide in the ecology of marine environments, especially the coastal zones. Without diminishing the positive importance of the marine seaweeds, it can be admitted that some have a negative impact through biofouling, habitat invasion and creating simple nuisance problems (such as unwanted beach drift). The tremendous diversity in biology, morphology and life history of the organisms known as the algae, as well as their polyphyletic evolutionary history, make a simple, practical definition of the group impossible (see, for example, Mattox and Stewart, 1984; Bold and Wynne, 1985; van den Hoek, 1992; for a review of algal classification through the first half of this century see Papenfuss, 1955,1957). They comprise three distinct groups of eukaryotic organisms: the green, red and chromophyte algae (the last group includes the brown algae), each of which possesses plastids of unique pigmentation and ultrastructure. At the highest taxonomic level algae have been traditionally treated as divisions (or phyla) within either the Kingdom Plantae or Protista (e.g. Margulis and Schwartz, 1988), but molecular approaches have changed our understanding of phylogenetic relationships even at these levels (see below).