Sareomycetes cl. nov.: A new proposal for placement of the resinicolous genus Sarea (Ascomycota, Pezizomycotina)

Abstract

Resinicolous fungi constitute a heterogeneous assemblage of fungi that live on fresh and solidified plant resins. The genus Sarea includes, according to current knowledge, two species, S. resinae and S. difformis. In contrast to other resinicolous discomycetes, which are placed in genera also including non-resinicolous species, Sarea species only ever fruit on resin. The taxonomic classification of Sarea has proven to be difficult and currently the genus, provisionally and based only on morphological features, has been assigned to the Trapeliales (Lecanoromycetes). In contrast, molecular studies have noted a possible affinity to the Leotiomycetes. Here we review the taxonomic placement of Sarea using sequence data from seven phylogenetically informative DNA regions including ribosomal (ITS, nucSSU, mtSSU, nucLSU) and protein-coding (rpb1, rpb2, mcm7) regions. We combined available and new sequence data with sequences from major Pezizomycotina classes, especially Lecanoromycetes and Leotiomycetes, and assembled three different taxon samplings in order to place the genus Sarea within the Pezizomycotina. Based on our data, none of the applied phylogenetic approaches (Bayesian Inference, Maximum Likelihood and Maximum Parsimony) supported the placement of Sarea in the Trapeliales or any other order in the Lecanoromycetes. A placement of Sarea within the Leotiomycetes is similarly unsupported. Based on our data, Sarea forms an isolated and highly supported phylogenetic lineage within the "Leotiomyceta". From the results of our multilocus phylogenetic analyses we propose here a new class, order, and family, Sareomycetes, Sareales and Sareaceae in the Ascomycota to accommodate the genus Sarea. The genetic variability within the newly proposed class suggests that it is a larger group that requires further infrageneric classification.

Keywords: Ascomycota; Sarea difformis; Sarea resinae; Sareaceae fam. nov.; Sareales ord. nov.; Sareomycetes cl. nov.; new taxa; resinicolous fungi; taxonomy.

Fig. 1.

Light micrographs of Sarea difformis and S. resinae. A. Ascomata of S. difformis and B. S. resinae; C. Young ascoma of S. resinae arising on a fresh resin flow; D. Cross-section of S. resinae showing hyphal growth into the liquid resin; E. Ascus and paraphyses of S. difformis; F. Young ascus of S. difformis; G. Asci and paraphyses of S. resinae; H. Young ascus of S. resinae. Scale bars: 1 mm (A, B), 500 μm (C, D), 10 μm (E, G), 5 μm (F, H).

Fig. 2.

Phylogenetic relationships of Sarea, Trapeliales and Helotiales based on two ribosomal genes (ITS, nucLSU) obtained from Bayesian, Maximum Likelihood and Maximum Parsimony (MP) analysis. Posterior Probabilities (PP), ML- and MP-Bootstraps are represented by the first, second and third numbers associated with internodes. Branches in bold indicate PP ≥ 95 %, and both ML and MP bootstrap values ≥ 70 %. Double lined branches indicate significant support obtained by two out of the three analyses. Scale = number of substitutions per site.

Fig. 3.

Phylogenetic relationship of Sarea and Lecanoromycetes based on six genes (ITS, mtSSU, nucSSU, nucLSU, mcm7, rpb1) obtained from Bayesian, Maximum Likelihood and Maximum Parsimony (MP) analysis. Taxon sampling broadly corresponds to the data set by Prieto et al. (2013). Posterior Probabilities (PP), ML- and MP-Bootstraps are represented by the first, second and third numbers associated with internodes. Branches in bold indicate PP ≥ 95 %, and both ML and MP bootstrap values ≥ 70 %. Double lined branches indicate significant support obtained by two out of the three analyses. Scale = number of substitutions per site.

Fig. 4.

Phylogenetic relationship of Pezizomycotina based on four genes (ITS, nucSSU, nucLSU, rpb2) obtained from Bayesian, Maximum Likelihood and Maximum Parsimony (MP) analysis. Posterior Probabilities (PP), ML- and MP-Bootstraps are represented by the first, second and third numbers associated with internodes. Branches in bold indicate PP ≥ 95 %, and both ML and MP bootstrap values ≥ 70 %. Double lined branches indicate significant support obtained by two out of the three analyses. Scale = number of substitutions per site.