1. A new arrangement of the collective families Lecanoraceae and Lecideaceae is proposed. 2. The following new families are described: Catillariaceae, Catinariaceae, Crocyniaceae, Eigleraceae, Fuscideaceae, Gomphillaceae, Haematommataceae, Harpidiaceae, Helocarpaceae, Koerberiellaceae, Lasiolomataceae, Lecidomataceae, Lopadiaceae, Megalariaceae, Micareaceae, Miltideaceae, Mycobilimbiaceae, Mykoblastaceae, Orphniosporaceae, Placolecidaceae, Porpidiaceae, Psorulaceae, Rhizocarpaceae, Rimulariaceae, Roccellinastraceae, Ropalosporaceae, Sarrameanaceae, Schadoniaceae, Schaereriaceae, Scoliciosporaceae, Sphaerophoropsidaceae, Squamarinaceae; Tephromelataceae, Tremoleciaceae, Xanthopsorellaceae. 3. The following new genera and generit names are introduced: Adelolecia, Cladidium (for Cladodium (Tuck.)Köf.-Gyeln. non Bridel). Clauzadea, Eiglera, Kiliasia, Megalaria, Poeltinula (for Melanospora Mudd non Corda), Xanlhopsorella (for Xanthopsora Schneider & Weber non Speg.). 4. New combinations are: Adelolecia pilati, Cladidium Ihamnitis. Clauzadea immersa, CI. monticola, Eiglera jlavida, Kiliasia athallina, K. episema, K. philippea, K. riparia, K. tristis, Megalaria grossa, Mycobilimbia sabuletorum, Placolecis opaca,Poeltinula cerebrina, Protoparmelia badia, Saccomorpha uliginosa, Xanthopsorella texana. 5. Lectotype species are selected for the following genera: Abacina Norman (A. alboatra), Amygdalaria Norman (A. pelobotryon), Calinaria Vainio (c. montana), Cladodium (Tuck.)Köf.-Gyeln. (Lecanora thamnitis), Courtoisia Marchand (c. exigua), Dimaura Norman (D. wahlenbergiij, Encephalographa Massalongo (E. elizae), Glaucomaria Choisy (Lecanora glaucoma), Ionaspis Th. Fries (I. epulotica), Lecaniella Jatta (L. cyrtella), Lecanoropsis Choisy (L. saligna), Lepadolemma Trevisan (L. ventosum), Mycobilimbia Rehm (M. obscurata). Oedemocarpus Trevisan (0. sanguinarius), Ophioparma Norman (0. ventosa), Placolecis Trevisan (P. balanina), Polyozosia 'Massalongo (P. poliophaea), Ricasolia Massalongo non Oe Not. (R. candicans), Skolekites Norman (S. candidus), Sporoblastia Trevisan (S. grifjithii), Thalloidima Massalongo (T. vesiculare), Zeora Fries (Lecidea orosthea). 6. Lecanorella josiae is a later synonym of Koerberiella wimmeriana and Lecidea conlraria is a later synonym of Eiglerajlavida. 7. In the past the Lecanoraceae and Lecideaceae had been families in which many very different genera with little evoluated thalli had been placed. But most of the genera differentiated to date belong to families, which have not been recognised up to now. Many genera of crustous lichens must be comprehended as isolated trunks of phylogenetically old groups of lichenized fungi (Honegger 1982). For classification of those genera one can use the characleristics of the asci. 8. There are more than one type of asci, which satisfy the definition of "type archaeasce" (LetrouitGalinou 1973). 9. There are mOre types of ascus construction as types of dehiscence. 10. As the numerous types of asci show, a thalline margin surrounding the apothecia in evolution has originated sometimes independemly of each other, also the proper margin as weil as the convex apothecium without margin. 11. As a rule the spore type within a family changes little or not at all (e.g. one-celled, oval, hyaline spores in Lecanoraceae, two- to manycelled, hyaline spores in Lecaniaceae, at least in an early stage of ontogeny halonate, hyaline, one-celled spores in Porpidiaceae.) 12. The Lecideaceae, at the moment a monotypic family, does not belong to the Lecanorineae. With greatest propability they will remain in future too a family with few genera. Lecidea is not a big genus. Most of the species up to now classified in Lecidea belong to other genera of other families. The only synonym to the generic name Lecidea is Cladopycnidium. The family name Lecideaceae has no synonym. 242 13. The Lecanoraceae contain several genera. Lecanora remains a large genus as long as the combination of characteristics "thallus crustous (0 effigurate, with coccal green algae, margin of apothecia ±lecanorine, asci of Lecanora-type, ascospores one-celled and hyaline" defines the genus. The family name Lecanoraceae has no synonym. 14. At least parts of the Parmeliaceae shoulJ be classified in Lecanoraceae. 15. The suborder Lecanorineae is limited to families, whose members have an apical apparatus with a Hmasse axiale". 16. Based on almost complete correspondence of ascus construction it seems justifiable to place the Pyxinaceae (syn. Physciaceae) in the Lecanorineae. 17. As far as we know now there are no obligately foliicolous Lecanorineae S.str. with a crustous thallus. 18. Some genera traditionally placed into Lecanoraceae have to be omitted from this family (e.g. Haeriwtomma, Squamarina, Solenopsora, Lecania). 19. We found clear differences in ascus construction between some genera, which in the past were thought to be closely related: Lecanora - Squamarina, Lecanora - Lecidea, Lecania - Catillaria, LecideaCatillaria, Bacidia - Mycobilimbia are not closely related genera. 20. Lecania - Speerschneidera (Lecaniaceae), Aspicilia - Agrestia (Aspiciliaceae ad int.) are further examples for a polyphyletic origin of foliose and fruticose lichens. 21. Also in Acarosporineae s. auct. closely related genera of Lecanorineae s. auct. are hidden. (e.g. Maronea - Fuscidea).