9508992 Chen Ascomycete fungi occur in terrestrial, freshwater (rivers, streams, lakes), and marine (estuaries, salt marshes, oceans) habitats around the world. The marine and many of the freshwater ascomycetes have distinctive morphological features of their spore bodies (the ascoma) that have traditionally been used to distinguish them from terrestrial ascomycetes. The same features occur in many different species and genera and may represent adaptations to the aquatic environment. It is difficult to determine whether two morpholgically similar species are similar because they share the same recent common ancestor or because they have both adapted to the aquatic environment in the same way despite different ancestries. Thus, evolutionary or phylogenetic relationships among terrestrial and aquatic ascomycete fungi remain obscure and poorly studied. In particular, whether marine fungi constitute a single major lineage or an assemblage of multiple lines that have adapted to saltwater conditions stands as a classic problem of mycology (the study of fungi). Drs. Chen, Shearer, and Crane of the Illinois Natural History Survey are analyzing new molecular sources of evidence, including nuclear ribosomal DNA sequencing, along with traditional morphological features in an attempt to determine the phylogenetic relationships among a large group of freshwater and marine fungi. Nucleotide sequences provide information about mutational differences between species that is independent of their morphology. Understanding the evolutionary relationships among ascomycetes is important because these fungi play an important role in our living world as decomposers of organic matter and as agents of plant and animal diseases, and as sources of medically and industrially significant compounds such as penicillin. Knowledge of the phylogenetic linkages among the ascomycetes allows us to search for new chemicals or to identify new pathogens from knowledge of their closest living relatives.
