Thelotrema oleariae Kantvilas, 2025

Thelotrema oleariae Kantvilas , sp. nov. ( Figs 3A View FIGURE 3 , 4A View FIGURE 4 )

MycoBank #MB 860368

Superficially most similar to T. suecicum (H.Magn.) P.James , and likewise with lepadinoid apothecia 0.3–1 mm wide, but distinguished from that species and indeed all others by the combination of 8-spored asci and the fusiform, faintly amyloid, grey-brown to brown, sparingly muriform ascospores, 35–78 × 9–15 µm, with 10–15 transverse and 0–1 longitudinal septa.

Type: — AUSTRALIA. Tasmania, Seagers Lookout, 42°40’S 146°38’E, 1190 m, on old Olearia pinifolia in subalpine woodland, 8 July 2024, G. Kantvilas 242/24 ( holotype — HO 621327)

Thallus whitish grey, effuse, smooth, c. 40–100 µm thick, to 15 cm wide; medulla I + red, inspersed with calcium oxalate crystals. Apothecia lepadinoid, to 0.3–0.8(–1) mm diam., scattered or crowded and fused together, initially semi-immersed and perithecioid, soon emergent, subglobose to hemispherical and mostly broadly adnate, with a round, ostiole-like opening c. 0.1–0.3 mm wide with an entire or radially cracked and scabrid margin; disc ± obscured entirely throughout development by the incurved thalline margin and/or the proper exciple, plane, grey-black, sometimes a little whitish-pruinose; proper exciple whitish or grey, usually with a ragged margin, in section 20–25 µm thick basally, to 50–60 µm thick apically, hyaline to pale yellowish, sometimes intensifying yellow in K, I + red; periphyses 10–15 µm long, 1.5–3 µm thick. Hypothecium 10–20 µm thick. Hymenium 130–170 µm thick, overlain by greyish granules that partly dissolve in K; paraphyses 1–1.5 µm thick, with apices not enlarged; asci 8-spored, elongate-clavate, 90–140 × 16–30 µm. Ascospores soon becoming grey-brown to brown, muriform at maturity, with 10–15 transverse and 0–1 longitudinal septa, fusiform, (35–)38– 56.0 –72(–78) × (9–)10– 12.5 –15 µm ( n = 65), faintly amyloid; locules roundish to ellipsoid; wall gelatinous, to 1.5–2 µm thick, swelling markedly in K, becoming undulate in post-mature spores.

Chemistry: —nil.

Etymology: —The specific epithet refers to the host of the new species, Olearia pinifolia ( Asteraceae ).

Remarks: —At first glance, with its neatly subglobose to hemispherical, emergent apothecia, this species resembles T. suecicum (H.Magn.) P.James or indeed any number of other lepadinoid species of the genus. It is distinguished by its distinctive, brown ascospores, with their consistently single, longitudinal septum across the central cells of the spore ( Fig. 4A View FIGURE 4 ). Within the broader context of the genus, this species is perhaps most similar to the tropical T. pachysporum Nyl. , or at least tends to key into that species in various published accounts. Certainly, the two species have similar-sized, comparably weakly amyloid ascospores, but in T. pachysporum , the longitudinal septa are developed only occasionally ( Mangold et al. 2009; Sipman et al. 2012). Furthermore, T. pachysporum also has inconspicuous, persistently immersed apothecia. A further taxon with brown, muriform ascospores is T. lepadodes Tuck. , but here the spores are larger and richly muriform with up to 5 longitudinal septa.

Like T. subdefectum Kantvilas (described below), this species is rare (or possibly overlooked) in Tasmania and known only from the papery bark of Olearia pinifolia in subalpine woodland ( Fig. 5 View FIGURE 5 ). This tree has not been specifically investigated for its epiphytes in the past, although it tends to be richly and conspicuously colonised by wet forest macrolichens, as well as being festooned with species of Usnea , notably U. capillacea Motyka and U. oncodes Stirt. However , it is a host that clearly merits further attention and, in addition to the two species of Thelotrema described in this paper, it is also known to support an undescribed species of Phlyctis .

Specimen examined: — AUSTRALIA. Tasmania, Pelion Plains, 41°50’S 146°03’E, 850 m, 13 March 1992, G. Kantvilas 143/92 (HO).