A review of algal (including cyanobacterial) symbionts associated with lichen-forming fungi is presented. General aspects of their biology relevant to lichen symbioses are summarized. The genera of algae currently believed to include lichen symbionts are outlined; approximately 50 can be recognized at present. References reporting algal taxa in lichen symbiosis are tabulated, with emphasis on those published since the 1988 review by Tschermak-Woess, and particularly those providing molecular evidence for their identifications. This review is dedicated in honour of Austrian phycologist Elisabeth Tschermak-Woess (1917–2001), for her numerous and significant contributions to our knowledge of lichen algae (some published under the names Elisabeth Tschermak and Liesl Tschermak).

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Fungi are one of the most diverse carbon source-assimilating organisms, living as saprobes, parasites and symbionts; they play an important role in carbon cycling in the ecosystem. A lichen thallus provides habitats for many non-lichenized fungi and usually contains large quantities of polyols. However, research has not been undertaken to identify carbon sources of lichen-inhabiting fungi. In this study, we isolated various lichen-inhabiting fungi from surface-sterilized Ramalina spp., Flavoparmelia caperata and Peltigera degenii, and demonstrated their ability to assimilate carbon sources, namely glucose, ribitol and mannitol. Several isolates efficiently assimilated mannitol and ribitol; however, most isolates could assimilate only mannitol or both ribitol and mannitol at low levels. It is suggested that there are different preferences and niche segregation of carbon sources among lichen-inhabiting fungi, and that this assemblage includes fungi with different lifestyles such as saprobes, endophytes and transient visitors.

Species in the genera Sirobasidium and Sirotrema (Tremellales, Tremellomycetes, Agaricomycotina, Basidiomycota) were described based on the morphology of teleomorph, and many of them lack both isolates of anamorphic yeast state and nucleotide sequence data. Strains of Sirotrema translucens and Sirobasidium japonicum were established for the rst time from basidiocarps collected in Japan. Also, an undescribed species in the genus Sirobasidium was isolated. Molecular phylogenetic analysis based on the sequences of D1/D2 region of large subunit ribosomal RNA gene (LSU D1/D2), ITS-5.8S ribosomal RNA gene (ITS), and small subunit ribosomal RNA gene (SSU) showed that St. translucens, which has been considered to be related to the genus Sirobasidium based on its basidial ontogeny, was placed in a phylogenetically separated clade including the genus Phaeotremella. The analysis also revealed that Sirobasidium sp. and Sb. japonicum, previously assumed to have a close a nity to the order Auriculariales, were members in the Tremellales. Sirobasidium sp. was characterised by its apiculate epibasidia and 2celled basidia, which is a unique combination of characteristics in the genus. In conclusion, we keep Sirobasidium japonicum in the Tremellales and propose Sirobasidium apiculatum sp. nov. and Phaeotremella translucens comb. nov.