The present study focused on the biodiversity and ecophysiology of aeroterrestrial green algae (Trebouxiophyceae, Chlorophyta) from mid latitudes, with major emphasis on the evaluation of environmental factors controlling growth and reproduction. The combination of molecular, morphological and physiological characters (e.g. polyols) leads to an improved taxonomy within this morphological simple organisms. Furthermore, mixotrophy is discussed as a competitive advantage within the ecosystem, as light microsensor measurements revealed radiation as a limiting factor in deeper biofilm layers.