THE LICHEN GENERA ARCTOCETRARIA, CETRARIA, AND CETRARIELLA (PARMELIACEAE) AND THEIR PRESUMED EVOLUTIONARY AFFINITIES

A circumscription of the lichen genus Cetraria Ach. s.s., presently co mprising 15 species, is made. The genus is characterized by oblong, ci triform conidia as well as characters of the ascus: a small axial body and a distinct amyloid ring structure in the tholus (the region betwe en the ocular chamber and the outer membranes in the apex of the ascus ). All fertile species of Coelocaulon Link are incorporated into Cetra ria, based upon the similarities in ascus structures and conidia. Two new combinations are made: Cetraria crespoae (Barreno & Vazquez) Karne f. and C. steppae (Sav.) Karnef. Two new genera, Arctocetraria Karnef. & Thell and Cetrariella Karnef. & Thell are described, each of which differs in ascus structure from Cetraria. The new combinations Arctoce traria andrejevii (Oxn.) Karnef & Thell, A. nigricascens (Nyl. in Kihl m.) Karnef. & Thell, Cetrariella delisei (Schaer.) Karnef. & Thell, an d C. fastigiata (Nyl.) Karnef. & Thell are made. Two additional specie s, earlier presumed to belong to Cetraria in the rather strict sense, are transferred to Tuckermannopsis Gyeln., mainly because of similarit ies in the ascus structure; the new combinations Tuckermannopsis inerm is (Nyl.) Karnef. and T. subalpina (Imsh.) Karnef. are made to reflect this change. The presumed evolutionary affinities of all of these tax a are discussed.