Placement of Triblidiaceae in Rhytismatales and comments on unique ascospore morphologies in Leotiomycetes (Fungi, Ascomycota)

Abstract

Triblidiaceae is a family of uncommonly encountered, non-lichenized discomycetes. A recent classification circumscribed the family to include Triblidium (4 spp. and 1 subsp.), Huangshania (2 spp.) and Pseudographis (2 spp. and 1 var.). The apothecia of these fungi are persistent and drought-tolerant; they possess stromatic, highly melanized covering layers that open and close with fluctuations of humidity. Triblidialean fungi occur primarily on the bark of Quercus, Pinaceae and Ericaceae, presumably as saprobes. Though the type species of Huangshania is from China, these fungi are mostly known from collections originating from Western Hemisphere temperate and boreal forests. The higher-rank classification of triblidialean fungi has been in flux due in part to an overemphasis on ascospore morphology. Muriform ascospores are observed in species of Triblidium and in Pseudographis elatina. An intense, dark blue/purple ascospore wall reaction in iodine-based reagents is observed in species of Pseudographis. These morphologies have led, in part, to these genera being shuffled among unrelated taxa in Hysteriaceae (Dothideomycetes, Hysteriales) and Graphidaceae (Lecanoromycetes, Ostropales). Triblidiaceae has been placed within the monofamilial order Triblidiales (affinity Lecanoromycetes). Here, we demonstrate with a three-gene phylogenetic approach that triblidialean fungi are related to taxa in Rhytismatales (Leotiomycetes). We synonymize Triblidiales under Rhytismatales and emend Triblidiaceae to include Triblidium and Huangshania, with Pseudographis placed within Rhytismataceae. A history of Triblidiaceae is provided along with a description of the emended family. We discuss how the inclusion of triblidialean fungi in Rhytismatales brings some rarely observed or even unique ascospore morphologies to the order and to Leotiomycetes.