Chapter 25

Not long after taxonomists recognized that among the saprolegniaceous fungi there were homologous groups possessing similar devices for insuring reproduction, they began industriously arranging these groups into hierarchical clusters to suggest relationships. Although the resulting phylogenetic schemes were fashioned around the relatively simple structure of the individual species, mycologists weighted differently the few available morphological similarities and differences. The family unit itself has not escaped attempts at phylogenetic speculation, and at the suprafamilial level, concepts of relationships have touched upon the origin of the fungi as a whole and of the Oomycetes (Mastigomycetes) in particular. In fact, more attention has been paid to the phylogenetic derivation of the larger taxonomic units in which the watermolds are placed than to the infrafamilial components. For example, Margulis (1968), who proposed that the eukaryotic cell arose through a series of specific symbioses with prokaryotes, suggested that animals and most fungi had a protozoan ancestry. On the other hand, Klein and Cronquist (1967) saw the Oomycetes as misfits in the otherwise cohesive unit of organisms recognizable as the fungi. These authors thought that oomycete ancestry was traceable to a different group of algae than that from which the fungi allegedly arose. Klein (1970) adopted essentially this same view. Chiefly, the phylogeny of the saprolegniaceous fungi has long been thought to be woven closely with some ancestral alga, and the morphological resemblance of watermolds to certain existing algal groups is usually advanced to testify to the soundness of this view. The propositions that derive the Saprolegniaceae (or Oomycetes in a broader sense) from algae has, of course, gone beyond simply selecting these chlorophyllous plants to be likely ancestors (C. E. Bessey, 1903; Klein, 1970). Now it is fashionable to remove the watermolds and their kind from the fungi altogether (Shaffer, 1975) and make of them honest bedfellows of the algae or some other groups (Whittaker and Margulis, 1978). Most persisting schemes advocate a direct algal ancestry for the Saprolegniaceae even though as early as 1881 de Bary (also in de Bary and Woronin, 1881) proposed a derivation of these fungi from peronosporaceous types, and a resting place for the group (de Bary, 1884) among the Ascomycetes. Early attempts at constructing phylogenetic sequences involving the Saprolegniaceae (and the Oomycetes) were of course not influenced by evolutionary thought or necessarily accompanied by the application of principles of progressive or regressive change. When, from a body of biochemical data, various relationships between watermolds and other organisms were discovered, evolutionary tendencies were considered. To be sure, the biochemical evidence for evolution in the saprolegnians (and thereby for phylogenetic sequencing) is far from broadly based. Nevertheless, interest in the phylogeny of these fungi refreshingly has been advanced by the admission that reasons for relationships can be found in aspects of behavior beyond mere morphological expression. As these biochemical studies have shown, simplicity in form and absence of a generous fossil record have made it difficult to construct phylogenetic schemes on evolutionary grounds, but have not made the task