Evolutionary trends in the Physciaceae

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 apriori 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 Physciaceae taxonomy. The taxonomic importance of conidial characters and of anatomical and ontogenetical spore characteristics need, therefore, a careful reconsideration in future. (C) 2001 The British Lichen Society.