A cladistic analysis of the Physciaceae, based on morphological and chemical data, is presented. In the resulting phylogenetic reconstruction two major clades are formed, one containing the foliose genera (Anaptychia, Dirinana, Heterodermia, Hyperphyscia, Physcia, Phaeophyscia, Physconia, Pyxine) and the fruticose Tornabea and the other containing the remaining, mainly crustose genera. Rinodina appears as paraphyletic with representatives both at the base of the tree, at the same level as the two major clades and at the base of the crustose clade. Also Mobergia has a basal position. The characters used and their distribution in the phylogenetic trees are discussed as well as their significance for the identification of monophyletic groups. The history of the family is also briefly hinted at and characters of importance for the recognition of new genera are surveyed. Relevant publications and the variation in secondary chemistry are presented in tables.

The current delimitation of the family Physciaceae has been generally accepted since detailed descriptions of ascus characters allowed for a more natural circumscription of lichenized ascomycetes. The generic relations within the family are, however, still controversial and depend on the importance different authors attribute to specific morphological or chemical characteristics. The aim of this paper is to describe ascospore ontogeny and to test the present taxonomic structure of the family against a parsimony-based cladistic analysis, which includes three different scenarios of a priori character weighting. A study of ascospore ontogeny revealed two distinct developmental lines. One line revealed a delayed septum formation, which clearly showed transitions from spores with apical and median thickenings to spores without apical, but still well developed median thickenings, and to spores without any thickenings. In the second developmental line with an early septum formation again taxa with no thickenings, median thickenings, and both median and apical thickenings were found. Although these characters were constant at a species level, median wall thickenings especially varied among otherwise closely related taxa. In the cladistic analyses the current taxonomic structure of the Physciaceae was only obtained after the five character groups, namely morphology and anatomy of the vegetative thallus, conidiomata and conidia, morphology and anatomy of the apothecia, ontogeny of the ascospores, and secondary metabolites of the thallus, were given equal importance, and after a subjective a priori weighting further increased the weight of the three characters ‘conidial shape’, ‘presence of apical thickenings’, and ‘spore septation delayed’. This structure was not supported by a cladistic analysis with equally weighted characters but reflected the biased character weighting of the present day Physdaceae taxonomy. The taxonomic importance of conidial characters and of anatomical and ontogenetical spore characteristics need, therefore, a careful reconsideration in future.

Three species of the Buellia epigaea-group, Buellia dijiana Trinkaus, Buellia georgei Trinkaus, Mayrhofer & Elix, and Buellia lobata Trinkaus & Elix, are described as new from Australia. The taxonomy, morphology, anatomy, chemistry, biogeography, and ecology of the three taxa are discussed. Characters which distinguish these species from the corresponding taxa in the northern hemisphere include secondary compounds (presence of xanthones) and filiform conidia. An extended key is provided for the whole Buellia epigaea group as well as other terricolous species of the genus.

A phylogenetic hypothesis based on nuclear ITS sequence data is presented for the family Physciaceae based on various representatives of foliose and fruticose groups and a number of species selected from the crustose genera Rinodina and Buellia s.l. The analysis supports the monophyly of the Physcia- and the Buellia- groups. This is in agreement with existing morphological evidence, particularly ascus characters. The Physcia group in the analysis includes the genera Anaptychia, Heterodermia, Hyperphyscia, Mobergia, Phaeophyscia, Phaeorrhiza, Physcia, Physconia, Rinodina, and Rinodinella, while the Buellia group includes Amandinea, Buellia and Diploicia. The genera Physcia, Phaeophyscia, Phaeorrhiza and Rinodinella were well supported as monophyletic groups. The support for Physconia is low. Rinodina and Buellia are not supported as monophyletic genera. In agreement with ascus and ascospore characters, Buellia lindingeri is placed within the Rinodina group, close R. lecanorina. The genus Amandinea as currently circumscribed was not supported as a monophyletic group. The analysis confirms results from other lichen families that foliose members have evolved more than once from crustose lichens. Rinodina and Rinodinella species without chemical compounds in their thalli form the sister group to Phaeophyscia, and both groups form a monophyletic assemblage. A more detailed analysis of the Physcia group is presented. Whilst several of the foliose genera were well supported, there is only poor support for traditionally accepted crustose genera. The taxonomic implications of these findings are discussed.

The identity of photobionts from 20 species of the Physciaceae from different habitats and geographical regions has been determined by ITS rDNA sequence comparisons in order to estimate the diversity of photobionts within that lichen group, to detect patterns of specificity of mycobionts towards their photobionts and as a part of an ongoing study to investigate possible parallel cladogenesis of both symbionts. Algal-specific PCR primers have been used to determine the ITS rDNA sequences from DNA extractions of dried lichens that were up to 5 years old. Direct comparisons and phylogenetic analyses allowed the assignment of Physciaceae photobionts to four distinct clades in the photobiont ITS rDNA phylogeny. The results indicate a diversity within the genus Trebouxia Puymaly and Physciaceae photobionts that is higher than expected on the basis morphology alone. Physciaceae photobionts belonged to 12 different ITS lineages of which nine could unambiguously be assigned to six morphospecies of Trebouxia. The identity of the remaining three sequences was not clarified; they may represent new species. Specificity at the generic level was low as a whole range of photobiont species were found within a genus of Physciaceae and different ranges were detected. The photobionts of Physcia (Schreb.) Michaux were closely related and represented one morphospecies of Trebouxia, whereas the algal partners of Buellia De Not and Rinodina (Ach.) Gray were in distant lineages of the ITS phylogeny and from several Trebouxia morphospecies. Photobiont variation within a genus of Physciaceae may be due to phylogeny, geographical distance or because photobionts from neighbouring lichens were taken (“algal sharing“). At the species level Physciaceae mycobionts seem to be rather selective and contained photobionts that were very closely related within one morphospecies of Trebouxia.