Using a temporal phylogenetic method to harmonize family- and genus-level classification in the largest clade of lichen-forming fungi

Although classification at supra-specific ranks is inherently arbitrary, comparable taxonomic ranks within clades can facilitate more consistent classifications and objective comparisons among taxa. Different circumscriptions of the hyper-diverse lichen-forming fungal family Parmeliaceae and widely different generic circumscriptions among authors have been proposed. For this study, we use a recently developed temporal approach that uses time-calibrated chronograms to identify temporal bands for specific ranks in Parmeliaceae and allied groups with the overarching goal of establishing a consistent, stable classification. A data set of 330 species, representing 73 genera in the family and 52 species of related families was used to address the circumscription of Parmeliaceae and its genera following the proposed temporal approach. Based on the results of this study, we propose a revised, temporal-based classification for Parmeliaceae, including all clades that share a common ancestor 102.13-112.88 Ma for families and a time window of 29.45-32.55 Ma for genera. Forty-five of the currently accepted genera in Parmeliaceae were supported in their current circumscription. Two subfamilies are accepted within Parmeliaceae: Protoparmelioideae Divakar et al. subfam. nov., including Protoparmelia and the resurrected genus Maronina, and Parmelioideae, including the bulk of genera in the family. The new genus Austromelanelixia Divakar et al. is proposed to accommodate a clade of southern Hemisphere species previously included in Melanelixia. Eumitria and tentatively Dolichousnea are resurrected as genera separate from Usnea. The following genera are reduced to synonymy: Allocetraria, Cetrariella, Usnocetraria, and Vulpicida with Cetraria; Arctocetraria, Cetreliopsis, Flavocetraria, Kaernefeltia, Masonhalea, Tuckermanella, and Tuckermannopsis with Nephromopsis; and the lichenicolous genera Nesolechia and Raesaenenia with the lichen-forming genera Punctelia and Protousnea, respectively. A total of 47 new combinations and three new names at the species level are proposed.