The generic position of Ustilago maydis, Ustilago scitaminea, and Ustilago esculenta (Ustilaginales)

Three species of smut fungi (Ustilaginales, Basidiomycota) of economic importance, Ustilago maydis on corn, U. scitaminea on sugar cane, and U. esculenta on Zizania latifolia, were investigated in order to define their systematic position using morphological characteristics of the sori, ultrastructure of teliospore walls, and molecular data of the LSU rDNA. LSU rDNA suggests that U. maydis and U. scitaminea belong to the genus Sporisorium. This has already been proposed for U. scitaminea, which develops sori with whip-shaped axes corresponding to columellae. U. maydis and U. scitaminea, like typical species of Sporisorium, present peridia and columellae in their sori. Therefore, U. scitaminea is called Sporisorium scitamineum. U. maydis, however, is not placed in the genus Sporisorium here, because ongoing investigation of molecular data from the ITS rDNA region yields contradictory results and because the name Sporisorium maydis is occupied by an imperfect fungus. U. esculenta is recognized as Yenia esculenta. This placement in a separate genus is based on molecular data and on unique teliospore ultrastructure, i.e. apically enlarged, partly confluent warts developing on a strongly folded plasmalemma, and the exosporium and endosporium forming part of the ornamentation. Part 193 in the series „Studies in Heterobasidiomycetes“ from the Botanical Institute, University of Tübingen.