Ustilaginomycetes on Osmunda

Sporulation, septal pore apparatus and host-parasite interaction between Us tilago osmundae and its host, the royal fern, were analyzed by light and el ectron microscopy using herbarium material and compared with findings in ot her species of Basidiomycota. The fungus produced thick-walled and thin-wal led hyphae on leaf surfaces and sporulated externally. Coralloid haustoria with numerous lobes were present only in epidermal cells. Hyphae in interce llular spaces were lacking. The septal pore apparatus was composed of a sim ple pore with two caps. Ustilago osmundae shares the type of septal pore ap paratus and host-parasite interaction with the Melanotaeniaceae of Ustilagi nomycetes. It differs from the other species of this family primarily in th e external sporulation and in the lack of intercellular hyphae. To accomoda te this unusual fungus in Melanotaeniaceae a new genus, Exoteliospora, is p roposed. Description and illustrations are given for Exoteliospora osmundae .