Species in lichen-forming fungi:balancing between conceptual and practical considerations,and between phenotype and phylogenomics

Lichens are symbiotic associations resulting from interactions among fungi(primary and secondary mycobionts),algae and/or cyanobacteria(primary and secondary photobionts),and specific elements of the bacterial microbiome associated with the lichen thallus.The question of what is a species,both concerning the lichen as a whole and its main fungal component,the primary mycobiont,has faced many challenges throughout history and has reached new dimensions with the advent of molecular phylogenetics and phylogenomics.In this paper,we briefly revise the definition of lichens and the scientific and vernacular naming conventions,concluding that the scientific,Latinized name usually associated with lichens invariably refers to the primary mycobiont,whereas the vernacular name encompasses the entire lichen.Although the same lichen mycobiont may produce different phenotypes when associating with different photobionts or growing in axenic culture,this discrete variation does not warrant the application of different scientific names,but must follow the principle"one fungus=one name".Instead,broadly agreed informal designations should be used for such discrete morphologies,such as chloromorph and cyanomorph for lichens formed by the same mycobiont but with either green algae or cyanobacteria.The taxonomic recognition of species in lichen-forming fungi is not different from other fungi and conceptual and nomenclatural approaches follow the same principles.We identify a number of current challenges and provide recommendations to address these.Species delimitation in lichen-forming fungi should not be tailored to particular species concepts but instead be derived from empirical evidence,applying one or several of the following principles in what we call the LPR approach:lineage(L)coherence vs.divergence(phylogenetic component),phenotype(P)coherence vs.divergence(morphological component),and/or reproductive(R)compatibility vs.isolation(biological component).Species hypotheses can be established based on either L or P,then using either P or L(plus R)to corroborate them.The reliability of species hypotheses depends not only on the nature and number of characters but also on the context:the closer the relationship and/or similarity between species,the higher the number of characters and/or specimens that should be analyzed to provide reliable delimitations.Alpha taxonomy should follow scientific evidence and an evolutionary framework but should also offer alternative practical solutions,as long as these are scientifically defendable.Taxa that are delimited phylogenetically but not readily identifiable in the field,or are genuinely cryptic,should not be rejected due to the inaccessibility of proper tools.Instead,they can be provisionally treated as undifferentiated complexes for purposes that do not require precise determinations.The application of infraspecific(gamma)taxonomy should be restricted to cases where there is a biological rationale,i.e.,lineages of a species complex that show limited phylogenetic divergence but no evidence of reproductive isolation.Gamma taxonomy should not be used to denote discrete phenotypical variation or ecotypes not warranting the distinction at species level.We revise the species pair concept in lichen-forming fungi,which recognizes sexually and asexually reproducing morphs with the same underlying phenotype as different species.We conclude that in most cases this concept does not hold,but the actual situation is complex and not necessarily correlated with reproductive strategy.In cases where no molecular data are available or where single or multi-marker approaches do not provide resolution,we recommend maintaining species pairs until molecular or phylogenomic data are available.This recommendation is based on the example of the species pair Usnea aurantiacoatra vs.U.antarctica,which can only be resolved with phylogenomic approaches,such as microsatellites or RADseq.Overall,we consider that species delimitation in lichen-forming fungi has advanced dramatically over the past three decades,resulting in a solid framework,but that empirical evidence is still missing for many taxa.Therefore,while phylogenomic approaches focusing on particular examples will be increasingly employed to resolve difficult species complexes,broad screening using single barcoding markers will aid in placing as many taxa as possible into a molecular matrix.We provide a practical pro-tocol how to assess and formally treat taxonomic novelties.While this paper focuses on lichen fungi,many of the aspects discussed herein apply generally to fungal taxonomy.The new combination Arthonia minor(Lücking)Lücking comb.et stat.nov.(Bas.:Arthonia cyanea f.minor Lücking)is proposed.

Delimiting species in Basidiomycota:a review

Species delimitation is one of the most fundamental processes in biology.Biodiversity undertakings,for instance,require explicit species concepts and criteria for species delimitation in order to be relevant and translatable.However,a perfect species concept does not exist for Fungi.Here,we review the species concepts commonly used in Basidiomycota,the second largest phylum of Fungi that contains some of the best known species of mushrooms,rusts,smuts,and jelly fungi.In general,best practice is to delimitate species,publish new taxa,and conduct taxonomic revisions based on as many independent lines of evidence as possible,that is,by applying a so-called unifying(or integrative)conceptual framework.However,the types of data used vary considerably from group to group.For this reason we discuss the different classes of Basidiomycota,and for each provide:(i)a general introduction with difficulties faced in species recognition,(ii)species concepts and methods for species delimitation,and(iii)community recommendations and conclusions.

Molecular phylogeny of the genus Sticta (lichenized Ascomycota: Lobariaceae) in Colombia

We present a molecular phylogenetic study of the lichen genus Sticta focusing on Colombia,using the ITS fungal barcoding gene for a total of 370 ingroup OTUs,with 322 newly generated sequences.The topology resulting from a maximum likelihood approach does not support current species concepts in Sticta,which use a morphological concept,but in contrast shows that similar morphodemes evolved multiple times independently within the genus.As a consequence,currently applied names such as S.fuliginosa and S.weigelii comprise numerous(up to more than 20)unrelated species-level lineages,which can be distinguished also phenotypically using previously unrecognized characters such as lobe configuration,lobe surface structure,tomentum type,and anatomy of the basal membrane of the cyphellae.We conclude that the genus Sticta contains about four to five times the number of species currently recognized.In Colombia alone,approximately 150 species of Sticta are present.

Revision of genera in Asterinales

The order Asterinales comprises a single family,Asterinaceae.In this study,types or specimens of 41 genera of Asterinaceae are re-examined and re-described and illustrated by micrographs.Seventeen genera,namely Asterina(type genus),Asterinella,Asterotexis,Batistinula,Cirsosia,Echidnodella,Halbania,Lembosia,Meliolaster,Parasterinopsis,Platypeltella,Prillieuxina,Schenckiella(=Allothyrium),Trichasterina,Trichopeltospora,Uleothyrium and Vizellopsis,are maintained within Asterinaceae.Echidnodes,Lembosiella,Lembosina,Morenoina,and Thyriopsi s are transferred to Aulographaceae based on morphological and molecular characteristics.Anariste is transferred to Micropeltidaceae,while Lembosiopsis is transferred to Mycosphaerellaceae.Placoasterella and Placosoma are morphologically close to taxa in Parmulariaceae,where they are transferred.Aulographina is placed in Teratosphaeriaceae,while Asterodothis,Asterinema,Dothidasteromella,Leveillella,Petrakina and Stephanotheca are transferred to Dothideomycetes,genera incertae sedis.Eupelte,Macowaniella,Maheshwaramyces,Parasterinella,and Vishnumyces are treated as doubtful genera,because of lack of morphological and molecular data.Aphanopeltis,Asterolibertia,Neostomella,Placoasterina,and Symphaster are synonyms of Asterina based on morphology,while Trichamelia,Viegasia,and Yamamotoa are synonyms of Lembosia.The characteristics of each family are discussed and a phylogenetic tree is included.