Unidentified lichenized fungi symbiotic with cyanobacteria collected in Japan were
found to exhibit characteristics similar to those of Trizodia acrobia, a fungus that
grows on Sphagnum and loosely associates with cyanobacterial colonies. The differences
between our samples and T. acrobia were its smaller asci and ascospores and its mode
of association with cyanobacteria, wherein our samples formed globose thalli within
which hyphal haustoria intruded into cyanobacterial cells, whereas the hyphae of T.
acrobia only loosely associate with cyanobacterial cells without forming any structure.
Moreover, thalli and ascomata of the collected specimens were found on the moist surface
of peeled logs and bryophytes, whereas T. acrobia grows exclusively on Sphagnum. Based
on our phylogenetic analysis using internal transcribed spacer and large subunit nuclear
ribosomal DNA regions and mitochondrial small subunit ribosomal DNA region of the
mycobiont, the collected specimens were grouped with T. acrobia and an unidentified
species of Trizodia. On the basis of these results, we describe T. silvestris to accommodate
the collected specimens. The cyanobacteria associated with T. acrobia have been reported
to be Nostoc without any molecular approach, whereas the cyanobiont of the collected
specimens were found to belong to Nostoc sensu stricto in the analysis based on 16
S rRNA gene. Because the genus Trizodia was not grouped with any other fungal genus
symbiotic with Nostoc, the symbiosis with Nostoc might have evolved independently
within the genus Trizodia from a loose association to the interaction with a differentiated
structure that could be regarded as lichen thalli.
