Thelidium mendax Pykaelae & Myllys, 2023

Pykaelae, Juha, Kantelinen, Annina & Myllys, Leena, 2023, Taxonomy of Thelidium auruntii and T. incavatum complexes (lichenized Ascomycota, Verrucariales) in Finland, MycoKeys 96, pp. 1-23 : 1

Thelidium mendax Pykaelae & Myllys sp. nov.

Figs 2C , 3H, J

Diagnosis.

Species morphologically rather similar to T. declivum and T. incavatum , but the involucrellum is on average longer.

Type material.

Holotype. Finland, Koillismaa, Salla, Oulanka National Park, Pikkuköngäs, shore of river Oulankajoki, high cliff, calciferous (dolomite) schistose rock outcrop, W-facing wall, on dolomite patch, 180 m a.s.l, 66°25'N, 29°08'E, 4 August 2010, J. Pykälä 39179 (H-9206536, GenBank accession number: OP901872).

Description.

Prothallus not visible. Thallus white to pale brown, endolithic to weakly rimose, algal cells, c. 4-7 μm. Perithecia 0.18-0.38 mm in diam., 1/2-1-immersed, often surrounded by thalline collar, leaving shallow to deep pits; c. 20-60 perithecia / cm2. Ostiole pale to dark, plane, c. 20-60 μm wide. Involucrellum apical to exceeding half of the exciple, c. 40-80 μm thick, appressed to the exciple or clearly diverging from it. Exciple 0.18-0.36 mm, wall dark brown to black, rarely pale, c. 20-30 μm thick. Periphysoids c. 40-60 × 1.5-2.5 μm. Asci c. 90-128 × 31-43 μm, 8-spored. Ascospores 3-septate, (34.8-)36.1-40.1-44.1(-51.0) × (11.8-)12.8-13.4-14.0(-14.9) μm (n = 48), perispore 1-1.5 μm thick in few spores.

Habitat and distribution.

The species is known from three localities, two in NE Finland, in the parishes Kuusamo and Salla, and one in Juuka in central eastern Finland. Thelidium mendax grows on calcareous rocks and calciferous (dolomite) schistose rocks. Two collection sites are affected by spring flooding and may periodically be submerged.

Etymology.

The species is easily misidentified.

Notes.

Based on the ITS phylogeny, this species is closely related to T. declivum . It is also morphologically difficult to separate from that species. Thelidium mendax has, on average, longer involucrellum than in T. declivum . Thelidium mendax is here kept separated from T. declivum because this solution received high support value in the ITS phylogeny (99%). Within the species T. declivum and T. mendax have identical ITS sequences and the species have a clear barcoding gap (3% difference).

Polyblastia torrentis (Sweden. Torne Lappmark: Jukkasjärvi par., Abisko, Regio subalpina by the torrent, alt. 400 m, 29 July 1921, A.H.Magnusson (UPS!, syntype)) differs in less immersed perithecia (1/4-1/2-immersed) and thinner involucrellum (c. 30-40 μm thick).

Other specimens examined.

Finland, Koillismaa, Kuusamo, Juuma , Oulanka National Park , Jäkälävuoma, gorge, calciferous (dolomite) schistose rock outcrop, on bottom, shore of a pond, on dolomite coated stone, 200 m a.s.l., 66°15'N, 29°26'E, 16 August 2010, J. Pykälä 40152 (H); Pohjois-Karjala, Juuka, Petrovaara, Riihilahti S, calcareous rock outcrop, on W-facing wall, 190 m a.s.l, 63°09'N, 28°58'E, 13 July 2011, J. Pykälä 42502 (H), 42503 (H) .

Figures

Figure 2. A Thelidium declivum (holotype) B T. huuskonenii (holotype) C T. mendax (holotype) D T. pseudoauruntii (holotype) E T. sallaense (holotype) F T. toskalharjiense (holotype). Scale bars: 1 mm (A-C, E, F); 0.5 mm (D).

Figure 3. Drawn anatomical features of the newly described Thelidium species. Represented perithecial features are similar between T. huuskonenii and T. toskalharjiense, as well as between T. declivum and T. mendax; therefore, they are shown combined. Spores are represented as intermediate size for all species A perithecia of T. huuskonenii and T. toskalharjiense combined B spores of T. huuskonenii C spores of T. toskalharjiense D perithecium of T. pseudoauruntii E spores of T. pseudoauruntii F perithecium of T. sallaense G spores of T. sallaense H perithecia of T. declivum and T. mendax combined I spores of T. declivum J spores of T. mendax. Scale bars for perithecia are 100 μm, and for spores 20 μm. Illustration: A. Kantelinen