Evolutionary relationships among mucoralean fungi (Zygomycota): Evidence for family polyphyly on a large scale

Mucorales (Zygomycota) are ubiquitous, morphologically simple terrestrial f ungi that are united taxonomically by possession of a coenocytic mycelium u pon which nonmotile mitotic spores are produced asexually in uni- to multis pored sporangia, and zygospores, where known, are produced following fusion of sexually compatible hyphae. Here we report the first comprehensive phyl ogenetic analysis of essentially all genera of Mucorales (63 species, 54 ge nera and 13 families) based on partial nucleotide sequence data of nuclear small subunit (18S) ribosomal RNA and nuclear large subunit (28S) ribosomal RNA genes, translation elongation factor-1 alpha gene exons, and a morphol ogical data set consisting of 1826, 389, 1092 and 11 characters, respective ly. Individual and combined data sets were analyzed by unequally weighted m aximum parsimony (MP) to investigate evolutionary relationships among and w ithin mucoralean families. A Micromucor-Umbelopsis clade, traditionally inc luded in the Mortierellaceae, was identified as the basal sister-group to a ll other Mucorales. A major discovery of this study is that traditional fam ily-level classification schemes for this order appear to be highly artific ial as evidenced by polyphyly of four of the seven families containing two or more genera. As presently circumscribed, these four families include 83% of the Mucorales. In addition, the largest and best known genera, Mucor an d Absidia, were resolved as polyphyletic. The results provide a robust phyl ogenetic framework for additional evolutionary studies of the Mucorales.