Resolving the phylogenetic position of Caeoma spp. that infect Rhododendron and Chrysomyxa from China

Many rust fungi that infect Rhododendron belong to the genus Chrysomyxa or the anamorph genus Caeoma. Their morphological resemblance suggests a close taxonomical relationship, however, their phylogenetic relatedness remains unknown. To reveal the phylogenetic affinity and clarify informative morphological characters, we analyzed the sequences of the internal transcribed spacer region of the nuclear ribosomal DNA of 56 isolates representing four species of Caeoma and their allied genus Chrysomyxa, which infect Rhododendron from China. The analysis revealed that Caeoma and Chrysomyxa cluster in the same clade and intermix, thus new combinations in Chrysomyxa have been provided for Caeoma that infect Rhododendron. We also provide expanded descriptions and illustrations of the aecia of Chrysomyxa yunnanensis and the uredinia of Chrysomyxa zhuoniensis for the first time. This study advances our understanding of evaluating some asexually typified generic names of rust fungi using molecular data to determine their correct placement.