FUNGI, FLAGELLA AND PHYLOGENY

Osmotrophic eukaryotes with a cell wall during the assimilative phase are 'fungi': the term 'fungus' is an essentially physiological concept , thus flagellate fungi conforming to this definition are not 'pseudof ungi'. But mycologists may also work with flagellate organisms which a re phagotrophic or lack a plasmodial cell wall and, therefore, are not strictly 'fungi'. In fungi the flagellate stage is confined to planon ts (asexual zoospores and gametes). Flagellar form and function have m any conserved characteristics, but although ultrastructural diversity, particularly in kinetosome/flagellar root structure, has been intensi vely studied, other morphological features of the zoospore have been l ess thoroughly explored. The numbers, lengths, orientations and struct ural ornaments of flagella all provide data for biodiversity assessmen ts at the species and ecological levels. The structural and functional biodiversity of fungal flagella and zoospores are reviewed, particula rly with respect to the isokont/anisokont flagellar lengths and the is okont/heterokont flagellar ornaments oi the zoospore. The straminipilo us ornamentation has particular functional significance. Correlations between molecular biology and flagellar ultrastructure indicate that s everal independent phylogenetic lines have evolved flagellate fungi. T he strengths and weaknesses of the databases for these phylogenies are discussed in historical and current contexts.