Optimal Partitioning for Molecular Phylogenetic Inference and Generic Delimitation in the Cetrarioid Core Group (Parmeliaceae, Ascomycota)

The species diversity of lichenized fungi remains largely underestimated, yet the number of species in the cetrarioid core group of Parmeliaceae has remained stable while generic delimitations have been highly debated. Here, we performed a partitioned phylogenetic analysis incorporating secondary structure characters of three ribosomal loci (ITS, mtSSU, and nuLSU) combined with comprehensive phenotypic traits. Based on the results, we hypothesized that a Large Temporal Band (29.0–35.0 Mya) may serve as a baseline threshold for most generic divergences, corresponding to late-Oligocene global cooling and the primary cladogenesis of cetrarioid core lineages as documented in previous molecular dating studies. Additionally, we suggest a Small Temporal Band (14.0–18.0 Mya) for a subset of recently radiated genera that originated during the Mid-Miocene Climatic Optimum transition (~16 Mya). Two currently accepted genera (Cetraria and Nephromopsis) are largely supported in their current circumscriptions. Two new genera, Cetramelanelia and Tuckermanoides, are proposed to accommodate a clade of two species from Cetrariella and Tuckermanopsis platyphylla, respectively. Allocetraria is confirmed to resurrect as a genus separate from Cetraria, with Usnocetraria and Vulpicida treated as its synonyms. Foveolaria is reduced to synonymy with Nephromopsis. Ten new combinations and one new synonym at the species level are made. A dual-band temporal hypothesis for generic delimitation appears taxonomically reasonable for most macrolichens.