Generic concepts in parmelioid lichens, and the phylogenetic value of characters used in their circumscription

Abstract

AbstractThis article traces the changing systems in the classification of the parmelioid lichens from the early 19th century to the present day. Molecular phylogenetic approaches have enabled the relative importance of traditionally used characters to be objectively re-assessed, and led to the realization of the significance of others that had previously been passed over or dismissed; for example, differences in ascospore and conidium types or the cell-wall constituents. Information on the different characters employed is presented and assessed. It is concluded that characters related to thallus form or chemical products prove to be less informative at the generic level than has sometimes been assumed. Features requiring further study are identified, and in the light of experience in this group, lichenologists should be cautious in translating their results into formal taxonomies.