The diversity of lichen photobionts is not fully known. We studied here the diversity of the photobionts associated with , a sub-cosmopolitan genus ecologically important, whose photobionts belong to the green algae genus . The genetic diversity of was screened by using the ITS rDNA and actin type I regions in 223 specimens and 135 species of collected all over the world. These data, added to those available in GenBank, were compiled in a dataset of altogether 545 sequences occurring in 172 species of . A high diversity of associated with was found. The commonest photobiont lineages associated with this genus are , , and . Analyses of partitioned variation were carried out in order to elucidate the relative influence on the photobiont genetic variation of the following factors: mycobiont identity, geographic distribution, climate, and mycobiont phylogeny. The mycobiont identity and climate were found to be the main drivers for the genetic variation of . The geographical distribution of the different lineages was described. Some lineages showed a clear dominance in one or several climatic regions. In addition, the specificity and the selectivity were studied for 18 species of . Potentially specialist and generalist species of were identified. A correlation was found between the sexual reproduction frequency of the host and the frequency of certain OTUs. Some lineages co-occur with higher frequency than randomly expected in the species.
