Crittendenia gen. nov., a new lichenicolous lineage in the Agaricostilbomycetes (Pucciniomycotina), and a review of the biology, phylogeny and classification of lichenicolous heterobasidiomycetes

Abstract

The lichenicolous ‘heterobasidiomycetes’ belong in the Tremellomycetes (Agaricomycotina) and in the Pucciniomycotina. In this paper, we provide an introduction and review of these lichenicolous taxa, focusing on recent studies and novelties of their classification, phylogeny and evolution. Lichen-inhabiting fungi in the Pucciniomycotina are represented by only a small number of species included in the genera Chionosphaera, Cyphobasidium and Lichenozyma. The phylogenetic position of the lichenicolous representatives of Chionosphaera has, however, never been investigated by molecular methods. Phylogenetic analyses using the nuclear SSU, ITS, and LSU ribosomal DNA markers reveal that the lichenicolous members of Chionosphaera form a monophyletic group in the Pucciniomycotina, distinct from Chionosphaera and outside the Chionosphaeraceae. The new genus Crittendenia is described to accommodate these lichen-inhabiting species. Crittendenia is characterized by minute synnemata-like basidiomata, the presence of clamp connections and aseptate tubular basidia from which 4–7 spores discharge passively, often in groups. Crittendenia, Cyphobasidium and Lichenozyma are the only lichenicolous lineages known so far in the Pucciniomycotina, whereas Chionosphaera does not include any lichenicolous taxa.

Tremella macrobasidiata and Tremella variae have abundant and widespread yeast stages in Lecanora lichens

“…Many Tremellomycetes have a dimorphic life cycle (Bandoni, 1995), but lichen‐associated Tremella species have been mainly studied when they form sexual fruiting bodies (basidiomata) on the lichen thalli or on/in the fruiting bodies (apothecia) of the ascomycete lichen symbiont. Thus, for most species only the filamentous life stage is well known and has been studied in detail (Diederich, 1996; Millanes et al ., 2021). However, in a recent study Tuovinen and colleagues (2019) showed that Tremella lethariae has a common and widespread yeast stage in thalli of Letharia and seems to enter the sexual cycle only rarely.…”

Species diversity of Basidiomycota

“…3). It is likely that the same trend will continue and the diverisity of dimorphic yeast-like taxa will be increase in the following ten years with more new species and genera described in the future (e.g., Millanes et al 2021). Exploration of as yet understudied regions and environments, as well as a more precise identification of cryptic morphologically indistinguishable species will substantially contribute to the species diversity in these fungi.…”

The yeast lichenosphere: high diversity of basidiomycetes from the lichens Tephromela atra and Rhizoplaca melanophthalma

“…The taxon sampling for each analysis was constructed based on the blast similarity sequence results and on the groups and sequences retrieved from previous phylogenetic studies; sequences of type materials were included when available (Supplementary Tables S1eS6). The taxon sampling of Agaricostilbomycetes was based on Millanes et al (2021) and Diederich et al (2022), that of Cystobasidiomycetes on Cernajov a and Skaloud (2019) and Millanes et al (2016a,b), that of Microbotryomycetes on Kachalkin et al (2019) and Yurkov et al (2016), and that of Ustilaginomycetes on Li et al (2017) and Wang et al (2015a). For the class Tremellomycetes, two separate MSAs were prepared, one for the order Tremellales and the other for Filobasidiales.…”

“…Dimorphism, i.e., the alternating formation of both a haploid unicellular yeast phase and a dikaryotic filamentous mycelium during their life cycle, is common in basidiomycetes (Bandoni, 1995;Boekhout et al, 2011;Oberwinkler, 1987;Sampaio, 2004;Millanes et al, 2021). In his revision about Pucciniomycotina yeasts, Oberwinkler (2017) suggested that, as is the case for other basidiomycete yeasts, the Cyphobasidiales yeasts in lichens are a part of the lifecycle of these basidiomycetes growing and forming large colonies inside the lichen thalli.…”