The systematics of the pyrenocarpous, partly lichenized ascomycete families Pyrenulaceae and Requienellaceae have been revised, using phylogenetic methods. The hamathecium structure provided a valuable character at the family level. The ascus tip structures have been closely examined as a possible source of new characters, but yielded only a few additional ones.
Cladistic analysis has been used as a tool to trace phylogenetic relationships in the Pyrenulaceae and the Requienellaceae. The proposed classification is a derivative of this. Moreover, the ancestors of the Pyrenulaceae and the Requienellaceae are hypothesized.
Based on cladistic analysis, it is assumed that the ancestor of the Pyrenulaceae was lichenized, and that a reversal (de-lichenization) took place in two separate evolutionary lines. The ancestor of the Requienellaceae was probably non-lichenized, and lichenization is assumed to have taken place several times within the family.
The main objective of this monograph is to elucidate the systematic position and phylogenetic relations of some insufficiently known groups of tropical lichens. Emphasis has been given to small groups with uncertain or disputed affinities, which were previously placed in or associated with the Pyrenulaceae. A revision of the large, monophyletic genus Pyrenula was not undertaken as its systematic position in the Pyrenulaceae is undisputed. Considerable effort has been put into the correct classification of species which have been excluded here from the Pyrenulaceae, many of which showed close relationships with either the Pleomassariaceae or the Trypetheliaceae.
The formerly unigeneric family Requienellaceae is emended here; it is proposed to include a much larger assemblage of mainly tropical lichenized taxa.
Species of the not closely related genus Mycomicrothelia have been frequently confused with some of the taxa studied here. Therefore a considerable amount of material of this genus was examined as well.