CLASSICAL MORPHOLOGY IN ZYGOMYCETE TAXONOMY

Classification of Zygomycetes has evolved with the description of new taxa and the rediscovery and redescription of known species. Taxonomy of orders in Zygomycetes is based on the morphology of the spore formi ng structures, sporangia and (or) sporangiola, or merosporangia. Some organisms produce only zygospores, azygospores, chlamydospores, or a c ombination of these structures. The occurrence and morphology of any o f the aforementioned structures and others (e.g., stolons and rhizoids , apophyses, branching pattern, fertile vesicles) are used to ascertai n the phylogenetic relationships in Mucorales. Our understanding of th e morphology, development, and phylogeny of Zygomycetes has been enhan ced by using microscopic observations and cladistic analysis of data s ets derived both from small subunit rDNA and morphology. Many morpholo gical characters (e.g., trophocyst, yeast cell formation) still appear to be reliable phylogenetic indicators while others (e.g., spore morp hology) are too variable. The value of zygospore morphology is reduced because the sexual spore has never been reported for many taxa. Many characters used to circumscribe mucoralean families probably do not in dicate relationships but still are useful in identification. Sporangio la should be considered indistinct from sporangia.