A new species of Mazosia (lichenised Ascomycetes: Roccellaceae) from Tasmania

Two species of Mazosia occur in Tasmania: the foliicolous, pantropical M. phyllosema and M. corticola, here described as new to science. The new species is characterised by a corticolous thallus containing psoromic acid and three-septate ascospores, 17–27 × 4–6.5 μm; it occurs in Tasmanian and Victoria.


Introduction
The genus Mazosia was introduced by Massalongo (1854), but was not generally taken up until the monumental work of Santesson (1952), who also discussed the confusion surrounding the application of this name and its taxonomic affinities. Following the work of Kalb & Vězda (1988), Lücking & Matzer (1996) and others, the genus is now included without controversy in the Roccellaceae with Enterographa, a likely close relative (Sparrius 2004), and positioned in a lineage that also includes Dichosporidium, Enterographa and Erythrodecton (Ertz et al. 2015). Mazosia is a typical element of tropical rainforests (Lücking 2008) and of the nine species reported for Australia (McCarthy 2020), only one, the subcosmopolitan M. phyllosema, extends into temperate latitudes (McCarthy et al. 2001). Of the more than 25 described species, the majority are foliicolous. Only six corticolous species are known, four confined to the Neotropics (Aptroot et al. 2014) and two to Japan (Sakata et al. 2017). Thus, the discovery of a corticolous species in the Nothofagus-dominated cool temperate rainforests of Tasmania can be considered truly remarkable. This species is described here as new to science.

Mazosia corticola
Chemistry. Psoromic acid detected by TLC; due to the thinness of the thallus, the characteristic P+ yellow spot test is unreliable.
Etymology. The specific epithet refers to the corticolous habitat ecology of the new species, unusual in a genus that comprises mostly foliicolous taxa.
Distribution and ecology. Mazosia corticola is known from four widely separated localities, three in Tasmania (all from different bioregions of the island) and one from Victoria. All are from the bark of the subdominant, cool temperate rainforest tree, Atherosperma moschatum, a tree with a persistently smooth, aromatic bark. Within rainforest vegetation, Atherosperma is known for supporting a distinctive suite of lichens. For example, there are the recently described Coenogonium atherospermatis and Megalaria planocarpa, and many crustose species from genera such as Pyrenula and Graphis which are confined to this host tree or almost so. The leaves of Atherosperma are also one of the principal hosts for the small number of foliicolous lichens that are found in Tasmanian cool temperate rainforest (McCarthy et al. 2001).
Notes. Remarkable as the habitat ecology of the new species is, there is no doubt that it belongs in Mazosia. It compared favourably with herbarium material of the generitype, M. rotula, M. phyllosema, the other taxon of the genus known to occur in the region, and several other species of Mazosia available for study, and with published accounts, notably those of Lücking (2008), Aptroot et al. (2014) and Sakata et al. (2017). Critical characters of the new species are the Trentepohlia photobiont, characteristic for corticolous taxa, as distinct from foliicolous taxa that contain Phycopeltis (Aptroot et al. 2014), the stratified construction of the apothecial margin, notably the layer of pigmented excipular hyphae overlain by a layer of crystals that is in turn overlain by a thalline layer (Lücking 2008), the particular ascus type (Fig. 2), the branched and anastomosing paraphyses, and the distinctive ascospores with an enlarged, uppermost median cell (Aptroot et al. 2014;Lücking 2008, Fig. 2). The presence of psoromic acid is also consistent with Mazosia, with several foliicolous species containing this substance.
Within the genus in general, M. corticola is closest to M. phyllosema with respect to ascospore size and gross morphology, but that species is foliicolous, contains Phycopeltis, and lacks secondary compounds. The corticolous species of Mazosia were comprehensively revised by Aptroot et al. (2014) and an expanded key to all species was published by Sakata et al. (2017), enabling ready comparisons with M. corticola. None of the taxa treated contain psoromic acid. Furthermore, the ascospores of M. carnea, M. endonigra, M. japonica and M. viridescens (syn. M. ocellata) are all smaller (collectively 15-20 × 3-6 µm), whereas those of M. leptosticta are larger (22-35 × 4-7 µm) (Aptroot et al. 2014;Sakata et al. 2017). Although the ascospores of M. bruguierae and M. corticola are of similar size, the former differs by having prominently elevated, rather than sunken, semi-immersed apothecia. Such apothecia are found not only in the new species, but also in M. leptosticta (larger spores) and M. japonica (smaller spores). On these characters alone, the new species stands as clearly distinct.   Mazosia phyllosema is characterised by a foliicolous habit, a Phycopeltis photobiont, rounded, immersed to adnate apothecia, 0.3-0.6 mm wide with a grey to black, plane disc, and fusiform, 3-septate ascospores, 15-26 × 4-5 µm [see Santesson (1952) and Lücking (2008) for comprehensive descriptions]. Tasmania appears to be at the ecological limits for this pantropical species. All collections comprise scattered, circular, grey-brown thalli, 1-2.5 µm wide, lacking a prothallus, with the Phycopeltis photobiont cells rectangular, oblong or rhomboidal, 12-20 × 6-12 µm and arranged in radiating plates. Apothecia are rare and immature, although they display the structure and asci characteristic of the genus. Conical, perithecia-like, emergent pycnidia are abundant with oblong macroconidia, 5-6.5 × 2 µm. These Tasmanian specimens are too scant for chemical analyses, although Lücking (2008) reports that this species contains no secondary substances.
Habitat and distribution. This species was first recorded for Tasmania by McCarthy et al. (2001). It occurs on the leaves of Atherosperma moschatum and the fronds of the fern Blechnum wattsii in the shaded understorey of rainforest. Associated species include Arthonia trilocularis, Byssoloma subundulatum, Fellhanera endopurpurea, Porina subapplanata and Trichothelium assurgens. Nowhere is it common.