Serusiauxia Ertz & Diederich, gen. nov.

Index Fungorum number: MB 834931; Facesoffungi number: FoF

Diagnosis: Distinguished from all known Pyrenulaceae genera by a sorediate thallus and chemistry with gyrophoric acid (C+ red soralia).

Description: See specific description below.

Etymology:- Named after Emmanuël Sérusiaux (Liège, Bel- gium) to honour his outstanding contribution to the lichenol- ogy of tropical regions.

Type: Serusiauxia inexpectata Ertz & Diederich.

Notes: – In our phylogenetic tree (Fig. 16), this lichen is sis- ter taxon to Lithothelium septemseptatum in a basal position within a main clade including also the genus Anthracothe- cium and several species of Pyrenula (including the generic type, P. nitida). This clade was defined as ‘Pyrenulaceae, Group 1’ in the phylogeny of the Pyrenulaceae by Gueidan et al. (2016). We wondered if we should include our new species within an enlarged concept of Pyrenula, which would then include the two Pyrenula clades recognized by Gueidan et al. (2016), the genus Anthracothecium and Lithothelium septemseptatum. However, the phylogenetic results strongly suggest that Pyrenula needs to be split into several genera. ‘Pyrenulaceae, Group 1’ is divided, with high support, in a clade comprising Pyrenula s.str. and Anthracothecium, and a second clade comprising our new species and Lithothelium septemseptatum. Following our tree, the two taxa are genetically rather distinct. Further, as long as the type of Lithothelium has not been sequenced, we cannot affirm that this clade refers to Lithothelium s.str. Finally, to our knowledge the new species is unique within the Pyrenulaceae by having a sorediate thallus and chemistry with lecanoric/gyrophoric acid, strongly resem- bling Dendrographa decolorans. We conclude that the description of a new genus Serusiauxia is the best option, supported by both molecular results and morphological characters.

Figure 16. Phylogeny of Pyrenulaceae based on a data set of mtSSU sequences that resulted from a RAxML analysis. Maximum likelihood boot- strap values are shown above or near internal branches. Internal branches that are considered strongly supported by both RAxML and Bayesian analyses are represented by thicker lines. The newly sequenced samples from Mauritius are highlighted, and their names followed by collecting numbers of authors, which act as specimen and sequence identifiers. A newly sequenced sample of Granulopyrenis from Iles Éparses is also added. The length of the branches represented by dashed lines was reduced by 50% for editing reasons.