Thelidium pseudoauruntii 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 pseudoauruntii Pykaelae & Myllys sp. nov.

Figs 2D , 3D, E

Diagnosis.

Species morphologically rather similar to T. auruntii , but the spores are smaller and the perithecia tend to be less immersed.

Type material.

Holotype. Finland, Kollismaa, Kuusamo, Oulanka National Park, Mataraniemi W, shore of Oulankajoki river, small dolomite rock outcrop, on SE-slope, 147 m a.s.l, 66°22'N, 29°20'E, 28 August 2011, J. Pykälä 45374 (H9220350, GenBank accession number: OP901877).

Description.

Prothallus not visible. Thallus pale greyish brown to medium brown, endolithic to rimose, algal cells c. 5-7 μm, with one dark brown thalline line. Perithecia 0.18-0.36 mm in diam., 1/4-1/2-immersed, not leaving pits to leaving shallow pits; c. 50-140 perithecia / cm2. Ostiole dark, depressed, c. 20-50 μm wide. Involucrellum covering half of the exciple, c. 40-70 μm thick, appressed to clearly diverging from the exciple. Exciple c. 0.17-0.24 mm, wall pale brown to usually dark brown, c. 15-20 μm thick. Periphysoids c. 20-25 × 2 μm. Asci c. 64-83 × 22-32 μm, 8-spored. Ascospores 0-1-septate, (21.3-)23.9-25.1-26.2(-26.6) × (8.6-)9.2-10.1-11.0(-12.2) μm (n = 23), perispore 1 μm thick present in some spores.

Habitat and distribution.

The species is only known from the type locality on small dolomite rock outcrop on the rivershore. The locality is likely to be under water during spring floods. Potentially suitable habitats for the species may be very rare in Finland.

Etymology.

The species resembles morphologically T. auruntii and is also closely related to the species based on the ITS sequences.

Notes.

The species is closely related to T. auruntii and T. sallaense . Only two specimens are known and from the same locality. We prefer to treat T. pseudoauruntii as a species separate from T. auruntii because of high support value (100%) in the ITS phylogeny. Furthermore, there is a clear barcoding gap (3%) between the species. The species have also different distribution areas. Thelidium pseudoauruntii seems to be absent from the calcareous fells of NW Finland, i.e., from the main distribution area of T. auruntii in Finland. Thelidium pseudoauruntii may be an eastern species with the main distribution area in North America and/or Russia. The specimens of T. pseudoauruntii have smaller spores than in T. auruntii and T. sallaense . Furthermore, the perithecia are less immersed. However, more material is needed to determine whether the species differs unambiguously morphologically from the related species.

Other specimens examined.

Finland, Koillismaa , Kuusamo , Oulanka National Park, Mataraniemi W, shore of Oulankajoki river, small dolomite rock outcrop, on dolomite stones, 145 m a.s.l., 66°22'N, 29°20'E, 28 August 2011, J. Pykälä 45371 (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