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Diederich, P./ Millanes, A.M./ Flakus, A./ Rodriguez-Flakus, P./ Etayo, J./ Wedin, M. 2022: Class Cystobasidiomycetes, order Cyphobasidiales. - Flora of Lichenicolous Fungi 1: 305-324. [RLL List # 272 / Rec.# 44172]
Abstract: The Cystobasidiomycetes was established by Bauer et al. (2006), as fungi characterized by the absence of fucose in their cell walls, and the presence of intranuclear spindle pole bodies during the metaphase. Recent phylogenetic studies have suggested the recognition of six orders within the group: Buckleyzymales, Cyphobasidiales, Cystobasidiales, Erythrobasidiales, Naohideales and Sakaguchiales (Spribille et al. 2016, Wang et al. 2015b, Zhao et al. 2017). Two fami-lies (Microsporomycetaceae and Symmetrosporaceae) are not included in any of these (Wijayawardene et al. 2020), and three genera, Cyrenella (Erythrobasidiales), Hasegawazyma (Erythrobasidiales) and Queiroziella (Cystobasidiales), do not yet have a family assignment in their respective orders (Crous et al. 2018, Wijayawardene et al. 2020). Kachalkin et al. (2019) and Wijayawardene et al. (2020) proposed to synonymize Cyphobasidiales under Erythrobasidiales. Kachalkin et al. (2019) based this decision on the unsupported phylogenetic affinity of the nuLSU sequences of Cyphobasidium to Cyrenella (Erythrobasidiales) and the uncertainly regarding the phylogenetic position of Cyphobasidium within the Cystobasidiomycetes. Although this reasoning is well based, their and our phylogenetic results also do not support the close relationship of Cyrenella and Cyphobasidium (see also single marker trees in Supplementary material). The analyses by Černajová & Škaloud (2019), based on seven genes, clearly separate Cyphobasidiales from Cyrenella although only three ribosomal markers were used for Cyphobasidium. Additional multigene phylogenies will be necessary to ascertain the systematics of Cyphobasidium and Cyphobasidiales. In this Flora, considering the phylogenetic results of Černajová& Škaloud (2019) and the lichen-inhabiting ecology of Cyphobasidium, we accept Cyphobasidiaceae and Cyphobasidiales to accommodate Cyphobasidium. The Cystobasidiomycetes comprise both sexual and asexual yeast forming taxa. As it is also the case in other ‘heterobasidiomycete’ groups, dimorphism is frequent in the group, and yeasts are a natural and expected part of the life cycle of these fungi. Examples in which both the yeast stage and the basidia-producing mycelial phase are known in nature are Nahoidea and Occultifur (Oberwinkler 1990). In some teleomorphs, including species in Bannoa, Erythrobasidium and Sakaguchia, basidia have been interpreted as conidial stages by some authors (Sampaio et al. 1999, Aime et al. 2006, Bauer et al. 2006). In other species, basidia have never been observed or are only found in culture (Hamamoto et al. 2002, Sampaio 2011, Fell 2011, Wang et al. 2015a, 2015b). Two genera with lichenicolous species are known in the Cystobasidiomycetes, Cyphobasidium (sexual and yeasts) and Lichenozyma (yeasts), while sequences related to Symmetrospora need further studies (Millanes et al. 2016, Spribille et al. 2016, Černajová & Škaloud 2019). The genus Cyphobasidium was described to accommodate lichen-inhabiting species in the Pucciniomycotina known to induce conspicuous galls on the host lichen thalli (Millanes et al. 2016). Spribille et al. (2016) discovered numerous yeast lineages from this genus that are widespread in lichens – especially in the cortex of species of the family Parmeliaceae. They also suggested that cystobasidiomycete yeasts could constitute a third component of the lichen symbiosis, being an essential partner in the formation of the lichen cortex. This is an interesting hypothesis that has since then received much attention from lichenologists and mycologists. Lücking et al. (2016) even introduced the new term ‘Hyperlichenized Fungi’ for Cyphobasidium. However, Černajová & Škaloud (2019) also sequenced these yeasts from ecorticate species, showing that the yeasts are not restricted to grow in the cortex, although they could still be part of a superficial lichen biofilm (Spribille 2018, Spribille et al. 2020). Recent genomic investigations have revealed enzymatic profiles in the basidiomycete yeast genomes not found in the lichen mycobiont (Tagirdzhanova et al. 2021), but the hypothetical role of the yeasts in the lichen symbiosis still remains to be tested. Oberwinkler (2017) considered that the basidiomycete yeasts in lichen thalli are simply the typical yeast colonies propagating mitotically, frequently produced by other dimorphic mycoparasites. We, for the time being, consider this explanation more plausible. Nevertheless, future investigations will surely shed light on these questions. Other authors have confirmed the presence of Cyphobasidium yeasts in Parmeliaceae and in other lichen families, such as Cladoniaceae, Lecanoraceae and Physciaceae (Černajová & Škaloud 2019, Mark et al. 2020). All this has nevertheless raised new challenges for the taxonomic characterization of this diversity, since Cyphobasidium yeasts have not yet been obtained in culture. Černajová & Škaloud (2019) described the monotypic genus Lichenozyma for a lineage of yeasts isolated from Cladonia, which Li et al. (2020) suggested to be synonymized under Microsporomyces. We still consider that the distinction of a different genus is justified. In the context of this Flora, however, we are not treating the yeast species individually, because we consider that a Flora should be a tool for knowing and identifying species, macroscopically and microscopically, in rare cases using molecular data (cryptic species). Therefore, both the yeast lineages in Cyphobasidium and also Lichenozyma pisutiana have been excluded. In the phylogenies reconstructed for the filamentous taxa in this Flora, neither Cyphobasidium, nor its phylogenetic position within the Cystobasidiomycetes get support. Additional specimens and molecular markers are needed to clarify the generic and species delimitation in Cyphobasidium. However, with the data at hand, we prefer to use conservatively wide concepts both for the genus and the species included.
Notes: New: Cyphobasidium buelliicola Diederich & W.R.Buck (on Buellia stillingiana from U.S.A.), C. crocodiicola Diederich & W.R.Buck (on Crocodia rubella from New Zealand), C. enterographicola Diederich, Ertz & Millanes (on Enterographa pallidella from Réunion), C. hypotrachynicola Diederich, Flakus, Etayo & Rodr.Flakus (on Hypotrachyna sp. from Bolivia, Colombia & Ecuador; H. vexans from Bolivia), C. lecaniicola Diederich, Ertz & Millanes (on Lecania naegelii from Belgium), C. puncteliicola Diederich & Millanes (on Punctelia graminicola from U.S.A.), C. ramalinicola P.Pinault & Diederich (on Ramalina fraxinea from France).
URL: https://ps.mnhn.lu/pub/FloraLichenicolousFungi1.pdf
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