Taxonomic revision of Ustilago, Sporisorium and Macalpinomyces

The three genera of smut fungi, Ustilago, Sporisorium and Macalpinomyces, form a complex that has eluded resolution by morphology (Langdon & Fullerton 1975, Vánky 1991, Piepenbring et al. 1998) and molecular phylogenetic analysis (Stoll et al. 2003, 2005). Two suggestions to reconcile the taxonomy of the complex have been proposed. The first was to break up the current taxa into several smaller genera and subgenera, and the second to unify the three genera into a single genus, Ustilago (Vánky 2002, Piepenbring 2004). The former solution is dependent on finding morphological synapomorphies that can delimit the genera, and the latter solution dismisses the wide morphological diversity within the group (McTaggart et al. 2012b). Synapomorphic morphological characters and host plant classification delimited clades in the Ustilago-Sporisorium-Macalpinomyces complex (McTaggart et al. 2012a). The current study defines these synapomorphic characters and proposes a new classification for many species currently placed in Ustilago, Sporisorium and Macalpinomyces. This approach preserves the well-known genera Ustilago, Sporisorium and Macalpinomyces, and enables the classification to reflect morphological diversity in the complex.