Thelidium incavatum Nyl. & Mudd, Man. Brit. Lich. 295 (1861)

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 incavatum Nyl. & Mudd, Man. Brit. Lich. 295 (1861)

Thelidium anisomerum = Thelidium anisomerum Hellb., Kgl. Svensk. Vet. Akad. Handl. 9(11):34 (1871). Type. Sweden, Gotland, Linde klint, C.Stenhammar (S-L-347!); Gotland in colle calcareo ad Linde, Stenhammar 34 (S-L-250!), syntypes.

Thelidium decipiescens = Thelidium decipiescens Vain., Acta Soc. Fauna Flora Fenn. 49(2): 129 (1921). Type. Finland, Ab, Finby [= Varsinais-Suomi, Salo, Särkisalo], Förby, in rupe calcaria, 20 August 1920, E.Vainio (TUR-V!).

Polyblastia sepulta =? Polyblastia sepulta A.Massal., Lotos 6: 81 (1856). Type: [Italy,] Circa Veronam ad saxa eocenica, A.Massalongo (VER!, syntype).

Type.

[ England] 282. Bilsdale, Yorkshire, W.Mudd (M-0207325!, syntype?) .

Description.

Prothallus not visible. Thallus white to grey, endolithic, in two specimens partly epilithic, slightly rimose, up to 0.1-0.15 mm thick, algal cells c. 4-6 μm. Perithecia 0.06-0.36 mm in diam., (1/2-)3/4-1-immersed, often thalline covered except apex, leaving deep pits; c. 20-160 perithecia / cm2. Ostiole pale to dark, plane, c. 20-40 μm wide. Involucrellum absent or apical, c. 30-60(-90) μm thick. Exciple 0.16-0.39 mm, wall dark brown to black, c. 15-25 μm thick, often with ostiolar neck, often pear-shaped. Periphysoids c. 40-50 × 1.5-2 μm. Asci c. 93-122 × 33-52 μm, 8-spored. Ascospores 3-septate, few spores submuriform with 5-7 cells, (32.3-)37.5-40.9-44.3(-49.4) × (12.2-)13.7-14.9-16.2(-18.1) μm (n = 78), rarely with a perispore c. 1 μm thick.

Habitat and distribution.

The species occurs in many localities in SW Finland on calcareous rocks and in lime quarries. It occurs on south- as well as on north-facing walls and on gentle slopes. More rarely, it grows on boulders, stones and pebbles. At present, more than 50 localities are known. Most localities are in the hemiboreal vegetation zone, a few in the southern boreal vegetation zone, only some tens of kilometres north of the limit of the hemiboreal zone. However, one separate locality occurs in Kuopio (former Juankoski) in eastern central Finland. Thelidium incavatum may be the most common species of Thelidium in SW Finland, together with T. minutulum Körb.

Notes.

The observed syntype of Polyblastia sepulta is somewhat similar to T. incavatum , and P. sepulta may be the oldest name available for the species. However, better material of P. sepulta is needed to confirm it. Furthermore, it is uncertain whether T. incavatum is the correct name for the Finnish specimens. The syntype in M differs in rimose thallus. However, several localities have been included in the protologue, and the specimen in M may be untypical for T. incavatum . The Finnish specimens fit well with the description of T. incavatum by Orange (2013).

If the Finnish specimens do not belong to T. incavatum , there are two other putative younger names available for them. Thelidium decipiescens was described from SW Finland ( Vainio 1921) and is morphologically similar to the sequenced Finnish specimens of T. incavatum . Already Vainio (1921) considered T. decipiescens to be similar to some material of T. incavatum . Thelidium anisomerum Hellb., described from Sweden, is also similar to T. incavatum .

Thelidium bavaricum Dalla Torre & Sarnth. has broader spores (Germany, Bavaria, an den aus den begrasten Boden hervorstehenden Dolomitblöcken oberhalb des Tiefenthales bei Eichstätt, April 1859, Arnold, in Arnold: Lich.. Exs. 87 (UPS-L-165297!, syntype): 30-48 × 15-20 μm, and submuriform spores may be more frequent.

The ITS sequence of the T. incavatum specimen, collected in the separate locality in eastern Finland, differs from the other sequenced specimens (98.5% similarity). The specimen also differs morphologically from the other specimens by less immersed perithecia (1/4-1/2-immersed) and thicker involucrellum (c. 70-90 µm thick). The spores may also be slightly shorter: 28.1-35.7 x 12.8-15.4 µm (n=15). It may represent a separate species but is now included in T. incavatum , awaiting more material.

Other specimens examined.

Finland, Varsinais-Suomi, Parainen (Korppoo), Åfvensår, Kaelklot island , calcareous rock outcrop on shore of the Baltic Sea , E-slope, on pebbles, 5 m a.s.l., 60°18'N, 21°31'E, 27 July 2009, J. Pykälä 35282 (H); Salo ( Särkisalo), Förby, 200 m S of lime factory, calcareous rock outcrop, on SW-slope, 60°05'N, 22°52'E, 8 September 2009, J. Pykälä 36857 (H); Salo ( Särkisalo), Förby, 200 m S of lime factory, abandoned lime quarry, on 40 cm high NW-facing wall, 18 m a.s.l, 60°05'N, 22°52'E, 8 September 2009, J. Pykälä 36867 (H); Parainen ( Iniö), Söderby, Biskopsoe island , calcareous rock outcrop on shore of the Baltic Sea, on N-slope, 8 m a.s.l, 60°20'N, 21°28'E, 9 June 2010, J. Pykälä 37971 (H); Parainen (Korppoo), Elfsjö, Stora Limskaer island , shallow abandoned lime quarry, on N-facing wall, 6 m a.s.l., 60°09'N, 21°26'E, 21 June 2010, J. Pykälä 38227 (H); Parainen (Houtskari), Björkö, Östra Långholm, Norrnäs, siliceous rock outcrop on shore of the Baltic Sea, NW-slope, on narrow calcareous vein, scarce, 9 m a.s.l., 60°15'N, 21°26'E, 29 June 2010, J. Pykälä 38399 (H); Parainen, Petteby, Kalkudden, abandoned lime quarry, on W-facing wall, 18 m a.s.l., 60°17'N, 22°10'E, 5 October 2011, J. Pykälä 46459 (H) ; Uusimaa, Hyvinkää, Myllykylä, Kalkkikallio , abandoned lime quarry, on N-facing wall, 100 m a.s.l, 60°36'N, 25°03'E, 7 July 2009, J. Pykälä 34722 & H. Rämä (H) ; Pohjois-Karjala, Kuopio (Juankoski), Siikajärvi, Huosiaisniemi , nature reserve, dolomite rock outcrop on shore of lake Ala-Siikajaervi , on gentle NE-slope, scarce, 97 m a.s.l., 63°12'N, 28°21'E, 26 July 2011, J. Pykälä 42871(H) .