Thelotrema subdefectum Kantvilas, 2025

Thelotrema subdefectum Kantvilas , sp. nov. ( Figs 3B View FIGURE 3 , 4C View FIGURE 4 )

MycoBank #MB 860370

Distinguished by the combination of lepadinoid apothecia, the (6–)8-spored asci and the ellipsoid, faintly amyloid, hyaline, muriform ascospores, 25–46 × 10–20 µm, with 5–8 transverse and 1–3 longitudinal septa.

Type: — AUSTRALIA. Tasmania, Lake Nicholls, slope north of hut, 42°39’S 146°38’E, 1000 m, on Olearia pinifolia in subalpine woodland, 27 December 2024, G. Kantvilas 263/24 ( holotype — HO 621639).

Thallus whitish, smooth and effuse, ecorticate, c. 20–30 µm thick, to 10 cm wide; medulla I + red, sparsely inspersed with calcium oxalate crystals. Apothecia lepadinoid, at first entirely immersed, discernible as round holes in the thallus surface, 0.1–0.2 mm diam., becoming semi-emergent, perithecioid, then at maturity hemispherical, broadly adnate, 0.7–1 mm wide, scattered or crowded, occasionally fused together; thalline margin smooth and entire, incurved, discoloured pale brownish, heavily inspersed with crystals of calcium oxalate; disc plane, pale grey, obscured ± entirely throughout development by the incurved thalline margin and/or the proper exciple; proper exciple whitish, entire or with a ragged margin, in section 15–20 µm thick laterally, 20–60 µm basally, pale yellowish, I + red; periphyses 10–20 µm long, c. 3 µm thick. Hypothecium 10–15 µm thick. Hymenium 110–140 µm thick, overlain by a brown or greyish epithecial layer unchanged in K; paraphyses 1–1.5 µm thick, with apices not enlarged; asci (6–)8-spored, elongate-clavate, 100–120 × 18–30 µm. Ascospores hyaline, muriform at maturity, with 5–8 transverse and 1–3 longitudinal septa, ellipsoid, 25– 32.1 –40(–46) × 10– 14.2 –18(–20) µm ( n = 65), weakly amyloid; locules irregularly roundish; wall gelatinous, to 0.5–2 µm thick, swelling markedly in K.

Chemistry:— nil.

Etymology: —The specific epith et al ludes to similarities between the new species and T. defectum Hale ex R.C.Harris.

Remarks: —This new species is characterised by its lepadinoid apothecia, and the relatively small, faintly amyloid, muriform ascospores. The common and widespread T. lepadinum (Ach.) Ach. differs by having 4–8-spored asci, and incrementally larger, non-amyloid ascospores, (50–)55.5– 80.7 –107(–110) × (10–)12– 18.1 –24(–30) µm, with up to 20 transverse and 5 longitudinal septa. Few species appear to possess a combination of characters similar to T. subdefectum . The North American T. defectum Hale ex R.C.Harris shares similar-sized ascospores (25–35(–45) × 12–15(–18) µm: Harris 1990, 1995), but differs clearly by its persistently rather immersed apothecia with a fissured, ± chroodiscoid, exfoliating thalline margin; its ascospores are also transversely septate up to 9–13 times. In the Australian flora, the most similar species is T. subadjectum Mangold , described from Queensland, which has similarly-sized, faintly amyloid ascospores but differs by having tiny, ± persistently immersed ascomata to 0.6 mm wide, with a split (rather than entire) thalline margin ( Mangold et al. 2009).

This species is known only from Tasmania where it has been collected from the papery bark of twigs and trunks of the tall shrub Olearia pinifolia ( Asteraceae ) in subalpine woodland ( Fig. 5 View FIGURE 5 ). This largely uninvestigated habitat is commonly dominated by typical wet forest lichens such as species of Pseudocyphellaria and the Pannariaceae . That this species has been long overlooked is in part due to its superficial resemblance to the common T. lepadinum , although its apothecia tend to be far less prominent and are immersed in thalline bulges that can sometimes be discoloured brownish. It is more likely to be confused with T. oleariae , which grows in identical habitats on the same host, but which differs by its greyish brown, sparingly muriform to submuriform ascospores.

Specimens examined: — AUSTRALIA. Tasmania: Pelion Plains, 0.5 km E of New Pelion Hut , 41°50’S 146°03’E, 850 m, 13 March 1992, G. Kantvilas 143/92 ( HO) GoogleMaps ; Gingerbread Hut , 42°08’S 146°06’E, 1260 m, 18 January 2025, G. Kantvilas 41/25 ( HO) GoogleMaps .