The generic concept and its early historical development until today’s more natural multi-character based concept is discussed. The modern generic concept for lichenized ascomy- cetes has traditionally been slightly different concerning crustose groups on the one hand and foliose and fruticose groups on the other. More studies of sexual reproductive structures in the large groups of lichens should presumably be carried out since it has been demonstrated recently that a considerable variation actually occurs in both asci and pycnidia in the cetrarioid genera. Some examples of difficult cases of evaluation of structural characters in relation to characters in the sexual reproductive structures in cetrarioid genera and the Teloschistaceae are also discussed.