Phylogenetic, taxonomic and biogeographical studies in the Pithophoraceae (Cladophorales, Chlorophyta)

The Aegagropila-clade is a unique lineage of algae within the large order Cladophorales and consists of poorly known taxa that mainly occur in brackish and freshwater environments. The clade is sister to the species-rich, primarily marine Cladophora- and Siphonocladus-lineages. Most of its members occur in narrow niches such as on the carapaces of freshwater turtles (some members of Basicladia), on freshwater snails and bivalves (monotypic Arnoldiella and several Basicladia species), on and endophytically in saltmarsh plants and mangrove pneumatophores (some members of Wittrockiella), or on marine intertidal snails (Cladophora conchopheria). Aegagropila linnaei is the best known representative of the lineage and has gained considerable scientific, cultural and economic fame due to the peculiar lake balls formed under specific conditions. The confused taxonomy of the Aegagropila-clade was clarified using methods of molecular phylogenetic inference, resulting in the re-instatement of the Pithophoraceae, descriptions of two new genera and several nomenclatural changes. Phylogenetic analyses led to an understanding of the evolution of the heterotrichous habit as an adaptation to changeable environmental conditions. In selected taxa, topics such as phylogeography and dispersal abilities, historical biogeography and glacial refugia, and ecology and declining populations were studied in detail