Topeliopsis obscura Kantvilas, 2025

Topeliopsis obscura Kantvilas , sp. nov. ( Figs 4D View FIGURE 4 , 8A View FIGURE 8 )

MycoBank #MB 860371

Separated from the virtually morphologically identical T. fatiscens Kantvilas by the 4–8-spored asci, hyaline, fusiform to narrowly ellipsoid, non-amyloid ascospores, 50–122 × 9–22 µm, with 9–19 transverse septa, and by usually containing traces of stictic acid.

Type: — AUSTRALIA. Tasmania, saddle c. 600 m E of Turrana Heights, 41°46’S 146°23’E, 1290 m, on Athrotaxis cupressoides in a small copse, 2 January 2024, G. Kantvilas 33/24 ( holotype — HO 618306).

Thallus crustose, discontinuous, forming diffuse patches many 10s of centimetres in extent, very thin and at most to c. 20 µm thick or, more typically, endophloeodal and discerned as a pale grey discoloration of the bark substratum; medulla I – or patchily I + pale violet-blue; photobiont Trentepohlia , with cells globose to ellipsoid, 11–18 × 7–17 µm, in clusters or short chains. Apothecia 0.5–1 mm wide, perithecioid, deeply immersed in the thallus and visible as elevated lumps pierced by a round, ostiole-like pore c. 0.05–1 mm wide, becoming emergent, with the pore widening and ultimately gaping; disc obscured throughout development, at length excavate and eroded; proper exciple fused to attached thallus fragments, ± free in the upper part, scabrid, brittle, dark grey, radially cracked, at length ± erect, dentate and exfoliating, in section 60–120 µm thick in the upper part, paraplectenchymatous, opaque dark brown, K ± olive-brown at the innermost and upper edges, less intensely pigmented to hyaline and I + pale violet within, basally opaque brown, 15–20(–35) µm thick; periphyses 10–25 µm long, 3–4 µm thick, often obscure. Hypothecium hyaline, 10–20 µm thick. Hymenium hyaline, non-amyloid, not inspersed, 180–220 µm thick; asci narrowly cylindrical to clavate, (125–)170–190 × 20–40 µm, 4–8-spored, non-amyloid, with a slightly thickened apex when young; paraphyses simple, 1.5–2 µm thick, straight to somewhat wavy, with apices unexpanded. Ascospores (50–)53– 82.8 –120(–122) × (9–)12– 16.8 –20(–22) µm ( n = 80), hyaline, sometimes becoming brownish and uneven in outline when over-mature, fusiform to narrowly ellipsoid, thinly halonate, I + reddish, transversely 9–19-septate; locules ellipsoid; wall 1–2 µm thick. Pycnidia not found; conidia developing from the breakdown of overmature ascospores, ellipsoid, 4–6 × 1.5–2 µm.

Chemistry: —stictic acid (usually in trace concentrations only) or nil; spot tests are unreliable. Traces of an unknown yellow pigment were detected in some extracts, but could have been due to a contaminant.

Etymology: —The species epithet refers to the new taxon being highly inconspicuous as well as alluding to the difficulty of interpreting some of its characters.

Remarks: —This species is one of several taxa that colonise the fibrous or flaky bark of mature trunks of the endemic conifer Athrotaxis cupressoides in small stands and copses of montane woodland ( Fig. 7 View FIGURE 7 ), have an essentially endophloeodal thallus and emergent apothecia that open by a rather ragged pore, and potentially occur sympatrically. Its morphological look-alikes are: T. fatiscens Kantvilas ( Trentepohlia photobiont; usually 2-spored asci; large, hyaline, muriform, amyloid ascopores; salazinic acid), T. kantvilasii Mangold & Lumbsch ( Trentepohlia photobiont; 8-spored asci; small, grey-brown, transversely septate, non-amyloid ascospores; stictic acid), Xerotrema megalosporum Sherwood & Coppins (doubtfully lichenised; 1-spored asci; large, hyaline, muriform, non-amyloid ascospores; containing no lichen substances); and an unnamed lichen of as yet unknown affinities but possibly allied to Leucodecton ( Trentepohlia photobiont; 1–3-spored asci; an opaque exciple lacking periphyses; large, hyaline, richly muriform, non-amyloid ascospores, 60–120 ×20–35 µm; no lichen substances). The identification of T. obscura requires observation of the characteristic, large, transversely septate ascospores, a task complicated by the fact that many apothecia are usually excavate and lack well-developed asci.

Further afield, there are several species of Topeliopsis that bear some superficial resemblance to T. obscura and also contain stictic acid. For example, T. patagonica Mangold & Lumbsch has similar-sized ascospores and 8-spored asci, but the apothecia are ± globose and superficial on the substratum, and its ascospores are amyloid ( Lumbsch et al. 2010). Other stictic acid-containing species, such as T. guaiquinimae (Sipman) Rivas Plata & Mangold , T. novaezelandiae (Szatala) Lumbsch & Mangold and T. juniperina van den Boom & Sipman differ by having muriform ascospores.

As with T. fatiscens and T. kantvilasii ( Kantvilas 2020) , the inclusion of the new species in Topeliopsis is undertaken with some caution, but after extensive comparison with other potential genera, Topeliopsis is seen as the “best fit” pending further study, preferably with molecular methods. Its general habit, excipular structure, chemical profile and anatomical details such as ascus type, paraphyses and presence of periphyses accord well with the genus as exemplified by the type, T. muscigena (Stizenb.) Kalb , T. decorticans (Müll.Arg.) Frisch & Kalb and their close relatives. However, the non-amyloid ascospores and the rather heavily pigmented exciple (at least in part) do not. In the future, the new species, T. kantvilasii and the unnamed taxon mentioned above may well prove to be better removed to a separate genus or genera.

Specimens examined: — AUSTRALIA. Tasmania: George Howes Lake , southern end, 41°47’S 146°17’E, 1150 m, 14 January 2022, G. Kantvilas 51/22 ( HO) GoogleMaps ; Lake Mackenzie , near car park, 41°41’S 146°23’E, 1100 m, 2 January 2023, G. Kantvilas 4/23 ( HO) GoogleMaps ; Blue Peaks, southern slope overlooking Middle Lake , 41°44’S 146°23’E, 1240 m, 2 January 2023, G. Kantvilas 7/23 ( HO) GoogleMaps ; Twisted Tarn , 42°40’S 146°34’E, 1120 m, 18 August 2024, G. Kantvilas 122/24 ( HO) GoogleMaps ; Lake Lexie , 41°46’S 146°22’E, 1265 m, 1 January 2025, G. Kantvilas 6/25 ( HO) GoogleMaps .