Verrucaria tenebrosa Pykälä, Launis & Myllys, 2018

Pykälä, Juha, Launis, Annina & Myllys, Leena, 2018, Verrucaria tenebrosa (Verrucariaceae), a new lichen species from Finland and Norway, and notes on the taxonomy of epiphytic taxa belonging to the V. hydrophila complex, Phytotaxa 361 (2), pp. 211-221 : 215-217

Verrucaria tenebrosa Pykälä, Launis & Myllys sp. nov. ( Fig. 2 , 3 )

MycoBank No.: 820096

Similar to Verrucaria infumata Nyl. , but involucrellum thicker, exciple wall often dark, and perithecia commonly thinly thalline covered. Type:— FINLAND. Koillismaa: Kuusamo, Juuma, Oulanka National Park, Hautaniitynvuoma, gorge, dolomite rock, NE-slope, beneath

NE-facing wall, on pebble, 66°15’N, 29°26’E, 190 m a.s.l., 21 August 2011, J. Pykälä 44686 (holotype H!).

Prothallus usually not visible, in one specimen dark brown, fimbriate, but weakly developed, in another specimen not clear whether fimbriae occur in the species or not. Thallus whitish grey (with green or brown flecks), pale greenish brown, pale brown, medium green, medium greenish brown, medium brown or dark brown, fleck-like, continuous or rarely rimose, on soft rock algal cells sometimes mixed with eroding rock particles, 10–60(–140) μm thick, not translucent when wet, cortex ca. 6–11 μm thick, cortical cells pale or brownish, algal cells 5–8 μm, irregularly arranged or in weakly defined columns. Perithecia 0.14–0.26 mm in diameter, 1/4–1/2(–3/4)-immersed, some perithecia superficial, not leaving pits, commonly thinly thalline covered (overmature naked); (40–)50–120 perithecia / cm 2. Ostiole inconspicuous, tiny, pale to dark, plane or depressed, in one specimen few pale projecting papillae present, 10–40 μm wide. Involucrellum to the exciple base level, 20–40 μm thick, may thicken to the base to 40–50 μm thick, appressed to the exciple or slightly diverging from the exciple. Exciple 0.13–0.22 mm in diameter, wall pale to dark brown. Periphysoids 14–27 × 1.5–2.5 μm, moderately branching. Asci 52–76 × 21–29 μm, 8-spored. Ascospores 0- septate, (16.1–)18.9–20.4–22.0(–24.8) × (7.4–)8.1–8.8–9.6(–10.8) μm (n=240).

Etymology: —Tenebrosus = gloomy, dark. The epithet refers to the “gloomy” shady habitats where the species usually grows.

Habitat and distribution: — Verrucaria tenebrosa is among the most shade-tolerant / shade-demanding species of Verrucaria . The species usually grows on or beneath N-facing cliffs on calcareous pebbles. Two specimens are from calcareous rock outcrops and one from a lime quarry. The only S-facing slope where the species was found is in a gorge close to the river shore. Verrucaria tenebrosa is widely distributed from southern Finland to northern Finland, but uncommon. The species has an eastern distribution in Finland; most localities are from the eastern part of the country. Verrucaria tenebrosa may be very rare in southern Finland. Even if V. tenebrosa has an eastern distribution in Finland, it was found from western Norway. The Norwegian specimen and the southernmost Finnish specimen (U, Pornainen, Pykälä 33015) slightly differ in their ITS sequences (by 5–6 bases) from the other specimens. The Norwegian specimen has an identical ITS sequence with the specimen 33015. Further data is needed to find out whether the Nordic population of V. tenebrosa can be divided into two groups with putatively different origin and distribution. The other locality of V. tenebrosa in southern Finland (Heinola) may be relictual, and the habitat is somewhat extreme. The species grows on pebbles under overhanging wall of a calcareous cliff. The only population of Henrica theleodes ( Sommerfelt 1826: 140) Savić, Tibell & Nav. -Ros. (in Savić & Tibell 2008: 244) in southern Finland occurs in the same locality.

The small species of Verrucaria growing on pebbles are often early colonizers typically found e.g. in lime quarries, but only one specimen of V. tenebrosa originates from a lime quarry. This species seems to grow mainly on pebbles with sites of long ecological continuity. Verrucaria tenebrosa seems to be rather insensitive to direct sunlight as well as very rarely growing in lime quarries. Such characteristics suggest the species may have clearly declined due to human activities, i.e. clear-cutting of forests close to calcareous rocks and lime mining.

Taxonomic notes: — Verrucaria tenebrosa clearly differs morphologically from the related species V. hydrophila , V. placida and V. dolosa . Verrucaria hydrophila has perithecia 3/4–1-immersed in the thallus, a thinner involucrellum clearly diverging from the exciple, a pale exciple wall, and a higher perithecial density (118–256 perithecia / cm 2) ( Orange 2013). Verrucaria placida has perithecia 3/4–1-immersed in the thallus, a thinner continuous thallus (25–65 μm thick), larger exciple (0.25–0.31 mm in diam.), and larger ascospores (mean 24.0 × 9.9 μm) ( Orange 2013). Verrucaria dolosa has smaller perithecia, a pale exciple wall, and clearly smaller ascospores (11–17 × 4–7 μm) ( McCarthy 1988). Verrucaria tenebrosa may instead be confused with several other species of Verrucaria particularly due to the high variation in the thallus colour between different specimens. In very shady habitats the thallus is whitish grey or pale brown but with green or brown flecks. In more exposed sites the thallus may be dark brown. Rather sparsely occurring perithecia (density 50–120 perithecia / cm 2) are typical for the species. Most species of Verrucaria with similar-sized perithecia have the perithecia occurring more densely (density 100–300 perithecia / cm 2).

Verrucaria tenebrosa is rather similar to V. infumata Nylander (1881: 452) (type: [ Sweden,] Holmia, 1852, W. Nylander (H-NYL 3367!)), which usually has a dark brown thallus. Verrucaria infumata has perithecia not thinly thalline covered, the exciple wall is pale, the involucrellum is thinner (15–30 μm thick), and a fimbriate prothallus is often well visible.

Verrucaria inaspecta Servít (1952: 359) ([ Sweden,] Västergötland, Osterplana par., E of church, on limestone, 31.7.1937, A. H. Magnusson 15830 (UPS-L-194244!, lectotype, designated by Pykälä & Breuss 2011); Västergötland, Osterplana, on limestone, 31.7.1937, A. H. Magnusson (PRM-859253!, isolectotype )) has smaller perithecia and narrower ascospores, the exciple wall is pale, the prothallus is absent, and the thallus is usually green or pale brown and not dark brown. Verrucaria lapidicola ( Orange 2014) is rather similar to V. inaspecta , but differs in the thalli consisting of goniocyst-like units and often a pale papillate ostiole.

Verrucaria floerkeana Dalla Torre & Sarntheim (1902: 524) has smaller ascospores (15–20(–22) × 6–9 μm), a pale exciple wall, and a thinner involucrellum (20–30 μm thick) ( Breuss & Berger 2010).

Specimens reported as V.fusca Pers. in Acharius (1810: 291) from Finland ( Pykälä & Breuss 2008) do not belong to V. fusca , but possibly to V. kalenskyi Servít (1951: 3) . These specimens are characterized by narrow ascospores compared to V. tenebrosa (15–22(–25) × 6–8 μm), usually a dark exciple wall, an ostiole often with pale, projecting papillae and more densely occurring perithecia (100–300 perithecia / cm 2).

The North American V. sordida Fink (in Fink & Fuson 1918: 273) (syntype: Indiana, Montgomery, on limestone along dry stream, 21.8.1917, Fink & Fuson (293) (MICH-00063176!)) differs in more densely occurring perithecia (200–220 perithecia / cm 2), smaller exciple (0.12–0.16 mm), and slightly broader ascospores (19–23 × 8–11 μm) (the protologue 16–22 × 9–12 μm, Fink & Fuson 1918).

The extreme shade specimens of V. tenebrosa with a pale thallus can probably not be identified with certainty without sequencing although even in very shady habitats the thallus of V. tenebrosa has brown or green flecks. Several species of Verrucaria with a pale thallus and a fairly similar morphology occur in Finland, but the taxonomy of these species is in need of revision. In shady habitats these species generally have a white or grey thallus, but in more exposed sites the thallus may sometimes be pale brown or have brown flecks.

Additional specimens examined: — FINLAND. Koillismaa: Salla, Oulanka National Park, Pikkuköngäs, shore of River Oulankajoki, high cliff, calciferous (dolomite) schistose rock outcrop, on SW-facing wall, with Sporodictyon schaererianum Massalongo (1852: 326) , 178 m a.s.l., 66°25’N, 29°09’E, 10.VIII.2009, Pykälä 36045 ( H); Kuusamo, Juuma, Oulanka National Park, Lammasvuoma, gorge, calciferous (dolomite) schistose rock outcrop, under overhanging SW-facing wall, on pebbles, 220 m a.s.l, 66°16’N, 29°25’E, 11.VIII.2009, Pykälä 36179 ( H); Kuusamo, Juuma, Oulanka National Park, Hautaniitynvuoma, gorge, dolomite rock outcrop, on high NE-facing wall, on dolomite pebbles, with Eiglera flavida ( Hepp 1861: 430) Hafellner (1984: 276) , Placynthium nigrum ( Hudson 1778: 524) Gray (1821: 395) and Protoblastenia rupestris ( Scopoli 1772: 363) Steiner (1911: 47) , 183 m a.s.l., 66°15’N, 29°26’E, 21.VIII.2011, Pykälä 44706 ( H); Pohjois-Karjala: Juuka, Polvela, Riihilahti E, calcareous rock outcrop, under N-facing wall, on pebbles, with Lepraria finkii (de Lesd. in Hue 1924: 334) Harris (1985: 45), 180 m a.s.l., 63°10’N, 28°59’E, 13.VII.2011, Pykälä 42471 ( H); Juuka, Polvela, Riihilahti E, calcareous rock outcrop, on overhanging N-facing wall, on pebbles, 180 m a.s.l., 63°10’N, 28°59’E, 13.VII.2011, Pykälä 42482, 42483 ( H); Enontekiön Lappi: Enontekiö, Kilpisjärvi, Saana, fell, steep NE-slope, dolomite rock outcrop, on dolomite pebbles, 820 m a.s.l., 69°02’N, 20°51’E, 11.VIII.2011, Pykälä 44129 ( H); Etelä-Häme: Heinola, Heinola, Mäyrämäki, NW-slope, Picea abies -dominated herb-rich forest, calcareous rock outcrop, under overhanging W-facing wall, on calcareous pebbles, 100 m a.s.l., 61°11’N, 26°08’E, 7.IX.2011 Pykälä 45611 ( H); Uusimaa: Pornainen, Laukkoski, Seppäkallio, Picea abies -dominated herb-rich forest, abandoned lime quarry, on small wall, scarce, 30 m a.s.l., 60°26’N, 25°25’E, 20.VII.2008, Pykälä 33015 ( H). NORWAY. Nørd-Trøndelag: Steinkjer, Mokk, Litl-Gaulstad, steep N-slope to the river, under overhanging wall of a calcareous boulder, on calcareous pebbles, 340 m a.s.l., 63°58’N, 12°07’E, 4.VIII.2015, Pykälä 48333 ( H).

Figures

FIGURE 2. Verrucaria tenebrosa (holotype).

FIGURE 3. Section of perithecium of Verrucaria tenebrosa (holotype).