Abstract
Lichen thalli provide a long-lived and stable habitat for colonization by a wide range of microorganisms. Increased interest in these lichen-associated microbial communities has revealed an impressive diversity of fungi, including several novel lineages which still await formal taxonomic recognition. Among these, members of the Eurotiomycetes and Dothideomycetes usually occur asymptomatically in the lichen thalli, even if they share ancestry with fungi that may be parasitic on their host. Mycelia of the isolates are characterized by melanized cell walls and the fungi display exclusively asexual propagation. Their taxonomic placement requires, therefore, the use of DNA sequence data. Here, we consider recently published sequence data from lichen-associated fungi and characterize and formally describe two new, individually monophyletic lineages at family, genus, and species levels. The Pleostigmataceae fam. nov. and Melanina gen. nov. both comprise rock-inhabiting fungi that associate with epilithic, crust-forming lichens in subalpine habitats. The phylogenetic placement and the monophyly of Pleostigmataceae lack statistical support, but the family was resolved as sister to the order Verrucariales. This family comprises the species Pleostigma alpinum sp. nov., P. frigidum sp. nov., P. jungermannicola, and P. lichenophilum sp. nov. The placement of the genus Melanina is supported as a lineage within the Chaetothyriales. To date, this genus comprises the single species M. gunde-cimermaniae sp. nov. and forms a sister group to a large lineage including Herpotrichiellaceae, Chaetothyriaceae, Cyphellophoraceae, and Trichomeriaceae. The new phylogenetic analysis of the subclass Chaetothyiomycetidae provides new insight into genus and family level delimitation and classification of this ecologically diverse group of fungi.
Highlights
Lichen symbioses give rise to unique structures
maximum likelihood (ML) and Bayesian analyses were found to be topologically concordant with each other (Fig. 2) and with previously and presently published phylogenetic inferences of Eurotiomycetes based on nucLSU and further combined nuclear and mitochondrial loci (Gueidan et al 2008, 2011, 2014; Teixeira et al 2017; Muggia et al 2015, 2016, 2017, 2019; Quan et al 2020)
The majority of sequences belonging to the endolichenic fungi are resolved into two main lineages, here named Pleostigmaceae fam. nov. and Melanina gen. nov., while the five remaining sequences are placed in the Cladophialophora clade within Herpotrichiellaceae (A1033, A1044, A1069, A1102 and A1123), one in Epibryaceae (A515), and one in Pyrenulales (A1133)
Summary
Lichen symbioses give rise to unique structures. The lichen thallus is that of a shape-determining fungus, the mycobiont, while one or more phototrophic microorganisms, the photobionts (green algae or cyanobacteria), are hosted extracellularly, entangled in a network of fungal hyphae (Hawksworth and Honegger 1994). The lichen thallus is an open, usually long-lived system, which with age provides a habitat for a growing number of additional microorganisms These comprise other fungi (filamentous and yeast-like), microalgae, and bacteria (Petrini et al 1990; Hofstetter et al 2007; Spribille 2018). Microscopy, culture-based experiments, and metabarcoding analyses have emphasized that many other fungi use lichens as a habitat in a hidden life cycle (Petrini et al 1990; Harutyunyan et al 2008; U’Ren et al 2012; Muggia et al 2016; Gueidan et al 2019). The lichen mycobiome changes with ecological and growth parameters of the lichen host, but precise interactions have still to be unraveled
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