Coreomyces (Laboulbeniales) in Sweden, with two new species

The genus Coreomyces (Laboulbeniaceae, Laboulbeniomycetes, Ascomycota) includes minute parasites on water boatmen (Corixidae, Hemiptera, Insecta). This taxonomic study is primarily based on freshly sampled corixids infected by Coreomyces from Sweden, although a few samples from Denmark and Turkey were also included. All records were verified using DNA sequence data from the internal transcribed spacer region and large subunit of the nuclear ribosomal DNA repeat region. We recognise four species, two of which are new to science: Coreomyces confusus H. Sundb. et al. sp. nov., C. corixae Thaxt., C. dextrorsus H. Sundb. et al. sp. nov. and C. macropus Thaxt. Coreomyces corixae is new to Denmark, Sweden and Turkey, while C. macropus is new to Denmark and Sweden. Coreomyces confusus is morphologically very similar to C. macropus and also occupies the same positions on the same host species, although it seems to be less common. Coreomyces dextrorsus resembles C. corixae morphologically but is usually considerably larger. It infects the same host species as C. corixae and also shares one of its positions on the host with C. corixae, although it is much more common in its species-specific position. All four species can inhabit two different yet distinct positions on the host. We observe that morphology is affected by the position on the host and that different species sharing the same position on the host tend to be difficult or impossible to separate on morphology only. We conclude that species circumscriptions in Coreomyces must be based on the integration of molecular and morphological data.