A Re-Examination of the Algal Class Xanthophyceae Based Upon 18S r RNA and rbc L Sequence Analysis

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Andersen DEB-9806743 The class Xanthophyceae includes a diverse assemblage of approximately 600 species of yellow-green colored algae. Some species are found in soil, but the majority are found in aquatic environments where they, and other algae, form the base of the food chain. With few exceptions, xanthophytes have not been studied using modern biological techniques. In fact many species have not been re-examined since they were described originally on the basis of light microscopic observations nearly 50 years ago. Historically, species have been classified based upon their "life form," i.e., 1) amoeboid cells, 2) walled cells lacking flagella, 3) flagellate cells, 4) filamentous cells, 5) walled cells held in a gelatinous envelope, or 6) multinucleate filaments that lack cross walls. The smaller flagellate species are generally regarded as being more primitive than the larger, filamentous and siphoneous forms. In preliminary phylogenetic analyses, we already have found that that some filamentous organisms are more similar to coccoid organisms than they are to each other. Similarly, several siphoneous organisms were not found to be closely related. Preliminary data also showed that a species currently placed in the Xanthophyceae should be classified within a completely different algal group. Anderson and Bailey, uniquely qualified for this study, will accomplish a long-overdue re-evaluation of the traditional classification of Xanthophyceae. The objectives are 1) to identify a group of species that can unequivocally be placed in the Xanthophyceae, 2) to construct a modern classification for the group, and 3) to re-classify elsewhere those species that belong in other algal groups.