The genus Porella is known for high phenotypic plasticity and rather ill defined species boundaries. Genetic and morphological data are analyzed for a broad sample of European and Macaronesian species (328 colonies collected in about 150 localities) in order to i) separate genetic entities and ii) identify the morphological characters that best define these entities. Nine species are recognized, including P. platyphylloidea from Canada, included for comparison. Many Porella colonies are multiclonal, attested by diversity found within colonies with intraspecific and interspecific polymorphisms, but also by male and female individuals found growing intermixed. At the intraspecific level, high levels of genetic variation are found, especially for P. canariensis, P. obtusata and P. platyphylla. Finally a revised key of the species is proposed.