Th. Fries, the eldest son of the mycologist Elias Fries, developed an early interest in lichens. He had full insight in the earlier research of lichens, particularly in Scandinavia, but at the same time developed new generic concepts in accordance with the Italian-German school (Massalongo and his followers). In this he was heavily critized by Nylander. Th. Fries may also be regarded as the father of Arctic lichenology, and he participated in several expeditions to the region (Finnmark, Spitsbergen, Greenland). His thoroughness, critical sense, and sound taxonomic judgements in the traditional morpho-floristic way combined with newer approaches, that of ascomata (particularly spore) anatomy, renewed lichenology and laid the foundation for its modern development.