Melanoxa, a new genus in the Urocystidales (Ustilaginomycotina)

A smut fungus, Melanotaenium oxalidis, forming dark-coloured spores in the leaves of Oxalis oregana (Oxalidaceae) was collected a few times in the USA. A similar smut fungus on Oxalis acetosella was recently collected in Slovenia. Teliospores, hyphal septations, cellular interactions and ITS and LSU rDNA sequences of these two smuts on Oxalis were examined and the results obtained were compared with each other and with findings in other members of the Ustilaginomycotina. The data show that the specimen from Slovenia is very close to Melanotaenium oxalidis, but represents a new species, and that the two Melanotaenium species occurring on Oxalis are members of the Urocystidaceae. Among the Urocystidaceae, they are morphologically very similar to Flamingomyces, Melanustilospora and Vankya species, but differ from them, and from all other Urocystidaceae, by their multilamellate teliospore walls. In addition, molecular phylogenetic analyses indicated good separation of the Melanotaenium species from Flamingomyces, Melanustilospora and Vankya. Accordingly, a new genus, Melanoxa, and a new species, M. oxalidiellae, are described, and a new combination, Melanoxa oxalidis, is proposed for Melanotaenium oxalidis.