Thelidium declivum 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 declivum Pykaelae & Myllys sp. nov.

Figs 2A , 3H, I

Diagnosis.

Differing from T. incavatum by the perithecia often less immersed in rock, the involucrellum present in most perithecia and the exciple wall is thicker, most difficult to separate from T. mendax but the involucrellum on average is shorter.

Type.

Finland, Koillismaa , Salla , Oulanka National Park , 400 m N of Savilampi, shore of river Savinajoki, dolomite rock outcrop, on NE-slope, scarce, 178 m a.s.l, 66°25'N, 29°10'E, 13 August 2009, J. Pykälä 36334 (H-9204893, holotype, UPS, isotype, GenBank accession number: OP901851 ) .

Description.

Prothallus not visible. Thallus white, grey or pale brown, endolithic to rarely thinly epilithic, algal cells c. 5-8 μm, in one specimen (type) surrounded by dark lines. Perithecia 0.12-0.44 mm in diam., 1/2-1-immersed, often surrounded by thalline collar, leaving shallow to usually deep pits; c. 20-80 perithecia / cm2. Ostiole pale to dark, plane to depressed, c. 20-50 μm wide. Involucrellum absent, apical or covering half of the exciple, 0-70 μm thick, appressed to the exciple or clearly diverging from it. Exciple 0.22-0.38 mm, wall dark brown to black, c. 25-40 μm thick, apex may be thickened to 50-70 μm thick. Periphysoids c. 30-50 × 1.5-2.5 μm. Asci c. 91-132 × 31-48 μm, 8-spored. Ascospores (1-2-)3-septate, few spores submuriform with 5-6(-8) cells, (32.3-)35.3-37.8-40.4(-44.4) × (12.6-)14.0-15.0-16.1(-17.3) μm (n = 69).

Habitat and distribution.

The species occurs in NE Finland, in the parishes of Kuusamo and Salla, on dolomite rock outcrops and boulders. The species may prefer rather shady habitats. Most localities are close to river shores.

Etymology.

The species prefers steep rock outcrops.

Notes.

This species was previously reported from Finland as T. larianum A. Massal. ( Pykälä 2010b). The type specimen of T. larianum A. Massal. (in calcaris ubique, Garovaglio, VER!) is in poor condition, and thus, the identity of the species cannot be solved. According to Zschacke (1934), the spore size of T. larianum is smaller: 25-36 × 11-15 μm than the size in the Finnish specimens. The protologue ( Massalongo 1855): "in circa Larium Lacum ad saxa calcareo-bituminosa Clar. Prof. Garov.", i.e., the locality is close to Lake Como, and the collector is S. Garovaglio. Thus, the climatic conditions of the type locality are likely to strongly differ from those in NE Finland, and it is likely that the Finnish specimens do not belong to T. larianum . Based on the Finnish distribution, it could be assumed that T. declivum may be an eastern species, which has its main distribution in Russia and/or in North America.

Polyblastia torrentis Servít (Sweden. Torne Lappmark: Jukkasjärvi par., Abisko, Regio subalpina by the torrent, alt. 400 m, 29.7.1921, A.H.Magnusson; UPS!, syntype) differs in less immersed perithecia (1/4-1/2-immersed) leaving shallow pits. Exciple may also be smaller (in studied perithecia c. 0.2-0.22 mm), but according to Servít (1953) the size of the exciple is c. 0.3 mm.

Thelidium declivum is difficult to separate from T. incavatum and the closely related T. mendax . Thelidium incavatum has predominantly fully immersed perithecia, and 3/4-immersed perithecia are usually overmature, whereas T. declivum has predominantly 3/4-immersed perithecia. Furthermore, the involucrellum is absent from most specimens of T. incavatum , whereas the involucrellum occurs in most perithecia, and in all studied specimens of T. declivum . Thelidium incavatum also has a thinner exciple wall: c. 15-25 μm thick. Thelidium mendax may differ in longer involucrellum, but more material is needed to determine whether this character can be used to separate the species from T. declivum .

Other specimens examined.

Finland, Koillismaa , Kuusamo , Oulanka , Putaanoja , 500 m W-NW of Hautala , dolomite rock outcrop, beneath N-facing wall, on boulder, 228 m a.s. l., 66°22'N, 29°25'E, 9 August 2009, J. Pykälä 35996 (H); Salla, Oulanka National Park , Savikoski 300 m N, shore of lake Savilampi , calciferous (dolomite) schistose rock outcrop, on N-facing wall, 175 m a.s.l, 66°25'N, 29°10'E, 10 August 2010, J. Pykälä 39640 (H); Salla, Oulanka National Park , Savilamminniemi, shore of lake Savilampi , cliff, calciferous (dolomite) schistose rock outcrop, on S-facing wall, 172 m a.s.l, 66°25'N, 29°10'E, 12 August 2010, J. Pykälä 39780b (H); Kuusamo, Oulanka, Putaanoja, 500 m W-NW of Hautala, dolomite rock outcrop, on NE-facing wall, 230 m a.s.l., 66°22'N, 29°25'E, 15 August 2010, J. Pykälä 39997 (H), 40037 (H), 40047 (H); Kuusamo, Oulanka National Park , Taivalköngäs, shore of Oulankajoki river , Picea abies -dominated herb-rich forest, dolomite rock outcrop, NE-slope, on dolomite boulder, 174 m a.s.l, 66°24'N, 29°11'E, 20 August 2011, J. Pykälä 44554 (H); Kuusamo, Oulanka National Park, Taivalköngäs, shore of Oulankajoki river, dolomite rock outcrop, on NW-facing wall, 165 m a.s.l, 66°24'N, 29°11'E, 25 August 2011, J. Pykälä 45123 (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