Trentepohliales are a group of both free‐living and lichenized algae, with most diversity occurring in tropical regions. Recent studies showed that the abundance of lichens with a trentepohlioid photobiont has been increasing in temperate habitats, probably because of global warming, which makes them an interesting study case. A detailed molecular study of the diversity of lichenized Trentepohliales, epiphytic as well as epilithic, was performed in three forests of north‐western Europe. Additional samples of lichens of the Arthoniales order (associating essentially with a trentepohlioid photobiont) from other European regions and from other continents were also sequenced. A total of 195 algal sequences were obtained. Phylogenetic analyses with rbcL and ITS loci were performed and associations between phylogenetic distances of photobionts and ecological factors (substratum, climate or Wirth indices, mycobiont taxonomy, and geographic location) were tested by variation partitioning and phylogenetic signal analyses. The high number of rbcL algal haplotypes found in some lichens or on different substrata revealed that the Trentepohliales diversity in extratropical regions was underestimated. The phylogenetic patterns showed selectivity of some photobionts in their fungal partner choice and vice‐versa, while others were linked with several haplotypes. Photobionts seemed to be less selective than mycobionts. The main factors influencing lichenized algal community were climate and mycobiont species. Coevolution between mycobionts and photobionts as well as switching between free living and lichenized lifestyles appeared to drive the evolution of Trentepohliales and might explain the high cryptic diversity observed, which might be changing in some regions due to climate change.

Cryptothecia aleurodes was considered to be a widespread, rare tropical lichen having white ascigerous areas and a crustose whitish-grey thallus containing norstictic acid. A revision of its type specimen from Guadeloupe and the study of recent specimens from Martinique proved that the species has been misunderstood. In this paper, Cryptothecia aleurodes is shown to have a K– and C+ red thallus containing notably gyrophoric acid as major secondary metabolite but lacking norstictic acid. A detailed description and illustrations are provided. The species is known with certainty only from the Caribbean and has probably a Neotropical distribution. Previous reports of C. aleurodes from the Seychelles and Thailand are shown to be misidentifications and reports from India are considered dubious.

Astrochapsa martinicensis is described as new to science. It is characterized by a whitish-farinose thallus, 6–8-spored asci, (4–)5–7(–9)-septate ascospores of (12.5–)14–24(–29) × (4.5–)5–6.5(–7) µm and a chemistry with one terpenoid and traces of UV+ substances. The new species was discovered among lichen specimens collected in 2013 on the island of Martinique (Lesser Antilles). A phylogenetic analysis using nuLSU sequences places the new species in the genus Astrochapsa, as sister species to an unidentified specimen from Venezuela. An identification key to all currently accepted Astrochapsa species is provided.