Photobiont association and molecular phylogeny of the lichen genus Chaenotheca

Chaenotheca Th. Fr. is associated with four different genera of photobionts , Dictyochloropsis, Stichococcus, Trebouxia, and Trentepohlia. The species of Chaenotheca consistently harbor only one photobiont genus. A molecular p hylogeny based on their ITS1-5. 8-ITS2 sequences of 16 species is presented . It contains Jive well supported clades. In two clades the species were on ly associated with Stichococcus, and one only with Trebouxia. In the other two clades two or three photobiont genera were present. Thus there is a par tial congruence between, photobiont association and cladogenesis in the gen us. Section Cystophora, characterized by its association with Trebouxia, an d sect. Allodium, with Stichococcus, are polyphyletic in the molecular phyl ogeny. The subgenera Chaenotheca and Cystophora are characterized by ascus shape and secondary chemistry. Two distinctive clades in the molecular phyl ogeny contain species referred to subg. Chaenotheca and two other distincti ve clades contain species referred to subg. Cystophora. However, one of the two clades containing species of subg. Chaenotheca has a clade of species belonging to subg. Cystophora as sister group, and the other one has all th e other species as sister group. These relationships, although only have we ak support.