Global warming is considered responsible for the increase of lichens associated with trentepohlioid algae in temperate regions. However, little is known about the diversity of Trentepohliales, a group of essentially tropical free-living and lichenized algae. A detailed study of the diversity of lichenized Trentepohliales was carried out in three forests of Western Europe. Additional samples of trentepohlioid lichens from other regions in the world were also used. A phylogenetic analysis using rbcL locus was performed, and associations between phylogenetic distances of photobionts and ecological factors (climate, geographic location, mycobiont host taxonomy and substratum) were tested by variation partitioning and phylogenetic signal analyses. Results highlighted an unexpected high diversity of the Trentepohliales in extratropical regions. The phylogenetic patterns showed selectivity of some algae in the mycobiont choice and vice-versa, while others had the ability to associate with several partners. Photobionts seemed to be less selective than mycobionts. The main factors influencing lichenized algal communities were fungal taxa and climate. Photobiont switching between mycobiont species as well as between lichenized and free-living lifestyles appeared to drive the evolution of Trentepohliales and might explain the high cryptic diversity observed.