Stop the Abuse of Time! Strict Temporal Banding is not the Future of Rank-Based Classifications in Fungi (Including Lichens) and Other Organisms

Abstract

Abstract Classification is the most important approach to cataloging biological diversity. It serves as a principal means of communication between scientific disciplines, as well as between scientists on one hand and lawmakers and the public on the other. Up to the present, classification of plants, fungi, and animals follows the fundamental principles laid out more than 250 years ago by Linnaeus, with less changes in the formalistic approach although with somewhat diverging rules for plants and fungi on one hand and animals on the other. Linnean classifications obey two fundamental rules, the binomial as basic format for species names, including a genus-level name and a specific epithet, and rank-based higher classifications, with the main ranks encompassing genus, family, order, class, phylum (division), and kingdom. Given that molecular phylogenies have reshaped our understanding of natural relationships between organisms, and following the cladistic principle of monophyly which defines groups but not ranks, it has been repeatedly argued that rank assignments are artificial and subjective, with the suggestion to either abandon rank-based classifications altogether or apply more objective criteria to determine ranks. The most fundamental of such approaches has been the correlation of rank with geological (evolutionary) age, first established by Hennig in the middle of the past century and around the turn of the millenium formalized as “temporal banding,” based on the advent of the molecular clock. While initially the temporal banding approach received less attention, in the past ten years several major studies mostly in vertebrates (birds, mammals) and fungi (chiefly lichenized lineages) have proposed novel classifications based on a strict temporal banding approach, partly with highly disruptive results. In this paper, the temporal banding approach is critically revised, pointing out strengths and flaws, and “best practice” recommendations are given how to employ this technique properly and with care to improve existing classifications while avoiding unnecessary disruptions. A main conclusion is that taxa recognized at the same rank do not have to be comparable in age, diversity, or disparity, or any other single criterion, but their ranking should follow integrative principles that best reflect their individual evolutionary history. In a critical appraisal of changes to the classification of Lecanoromycetes (lichenized Fungi) proposed based on temporal banding, the following amendments are accepted: Ostropales split into Graphidales, Gyalectales, Ostropales s.str., and Thelenellales; Arctomiales, Hymeneliales, and Trapeliales subsumed under Baeomycetales; Letrouitiaceae subsumed under Brigantiaeaceae; Lobariaceae and Nephromataceae subsumed under Peltigeraceae; Miltideaceae subsumed under Agyriaceae, and Protoparmeloideae and Austromelanelixia as new subfamily and genus within Parmeliaceae. The following changes are not accepted: Rhizocarpales split into Rhizocarpales s.str. and Sporastatiales (no information gain); Sarrameanales split into Sarrameanales s.str. and Schaereriales (no information gain); Carbonicolaceae subsumed under Lecanoraceae (topological conflict); Graphidaceae split into Diploschistaceae, Fissurinaceae, Graphidaceae s.str., Thelotremataceae (no information gain, topological conflict); Ochrolechiaceae split into Ochrolechiaceae s.str., Varicellariaceae, and Variolariaceae (no information gain, nomenclaturally incorrect); Porinaceae replaced by Trichotheliaceae (nomenclaturally incorrect); Ramalinaceae split into Biatoraceae and Ramalinaceae s.str. (no information gain, topological conflict); Stereocaulaceae subsumed under Cladoniaceae (nomenclaturally incorrect); Thrombiaceae subsumed under Protothelenellaceae (topological conflict); and all proposed genus level synonymies in Parmeliaceae. New fungal taxa: The new order Odontotrematales Lücking ordo nov. is established for the family Odontotremataceae s.str., based on topological grounds.