Phylogeny and taxonomy of Rhytisma -like species worldwide

Rhytisma Fr. is the type genus of Rhytismataceae (Rhytismatales, Leotiomycetes, Ascomycota). Rhytisma -like species include members of Cryptomyces , Rhytisma and Vladracula . They are parasites on leaves of broadleaf trees and cause tar spot diseases. In this study, a phylogeny based on the large subunit of the ribosomal rRNA gene (nrLSU) and the mitochondrial small subunit (mtSSU) is presented, including sequences of 39 newly collected specimens from East Asia, Europe, and temperate as well as tropical America. Based on analyses of morphology, phylogeny as well as host-specificity and diversification time estimates, the family Rhytismataceae sensu stricto is proposed, and eight genera are accepted in this narrow family, including four novel genera ( Densorhytisma , Fanglania , Johnstoniella and Shiqia ), the type genus Rhytisma , and the reinstated genera Lophodermina , Placuntium and Xyloma . Lophodermina clusters within the main Rhytisma clade in our analyses, but is divergent in morphological terms, not having large compound stromata. Thirty species are recognized, including seven novel species ( Fanglania hubeiensis , F. parasitica , Johnstoniella yunnanensis , Rhytisma japonicum , Rh. taiwanense , Xyloma globosum , and X. shennongjiaense ), fifteen new combinations ( Densorhytisma anhuiense , D. huangshanense , F. concova , F. himalensis , F. ilicis-integrae , F. ilicis-latifoliae , F. ilicis-pedunculosae , J. lonicerae , Rh. annuliforme , Shiqia menziesii , S. yuexiensis , X. filamentosum , X. maximum , X. muelleri , and X. polare ), one new name ( J. xylostei ), seven known species ( Lophodermina melaleuca , Placuntium andromedae , Rhytisma acerinum , Rh. americanum , Rh. punctatum , X. salicinum , and X. umbonatum ). In addition, seven immature specimens were studied but not assigned to existing species, herein referred to as Fanglania sp. 1, Johnstoniella sp. 1, Johnstoniella sp. 2, Placuntium sp. 1, Placuntium sp. 2, Rhytisma sp. 1, and Xyloma sp. 1. The systematic positions of Cryptomyces maximus , Cr. muelleri and Vladracula annuliformis are re-assigned based on phylogenetic analysis. One Rhytisma -like species from tropical America was segregated from Rhytismataceae s.str., thus a novel genus Neorhytisma was established to accommodate this species, with the one new combinations Neorhytisma panamense . The results of the molecular phylogenetic analysis indicate that Rhytisma -like species are host-specific at genus level. Apparently, Rhytisma -like species coevolved with their hosts, and Rhytisma -like species on Ericaceae seem to be in the process of host jumping. Morphological characteristics of ascomata are important for the delimitation of species and genera of Rhytisma -like species. This study provides a key to genera and species of recognized Rhytisma -like species worldwide.