Four new species of Verrucaria (Verrucariaceae, lichenized Ascomycota) from freshwater habitats in Europe

Verrucaria nodosa sp. nov. and V. rosula sp. nov. each have a thallus composed of initially discrete units which coalesce and overlap with age, forming an uneven crust. They are related species and similar in appearance, but the thallus units are coarser in Verrucaria nodosa, and the involucrellum is typically more regularly thickened than in V. rosula. Verrucaria placida sp. nov. has a smooth, subgelatinous thallus; it is related to V. hydrophila sp. nov. but differs in the larger ascospores and perithecia. It is not closely related to V. andesiatica but is morphologically similar, differing mainly in the narrower ascospores. Verrucaria hydrophila has been widely known as V. hydrela auct., non Ach. or V. denudata Zsch. nom. illeg. Verrucaria laevata Ach. is considered to be a nomen dubium.