Verrucaria lignicola Zschacke (1927: 55)

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 : 217-218

Verrucaria lignicola Zschacke (1927: 55)

Type:— Belgique, Spa Racines d’Alnus dans un ruisseau, 10 August 1904, M. Bouly de Lesdain (samml. Zschacke 4338) (syntype: B 600190155!).

Prothallus absent. Thallus grey, pale grayish brown, pale green, medium green or medium brown, thin, continuous, 20–50 μm thick, algal cells 5–8 μm, often in vertical columns. Perithecia 0.09–0.18 mm in diameter, (1/2–)3/4(– 1)-immersed, thinly thalline covered except apex; 140–280 perithecia / cm 2. Ostiole tiny, pale, plane or projecting papillae, rarely depressed, 10–30 μm wide. Involucrellum to the exciple base level, 15–30 μm thick, appressed to the exciple or slightly diverging from it, occasionally incurving under the exciple. Exciple 0.09–0.17 mm in diameter, wall pale, occasionally darkening. Periphysoids 8–20 × 2–2.5(–3) μm. Asci ca. 41–51 × 18–21 μm, 8-spored. Ascospores 0-septate, (13.7–)15.5–17.3–19.1(–20.7) × (5.8–)6.6–7.2–7.7(–8.3) μm (n=74).

Habitat and distribution: —The species grows on lake and brook shores, on bases and exposed roots of deciduous trees. Besides the type locality in Belgium ( Zschacke 1927), the species has been reported from Finland ( Pykälä & Breuss 2009), France ( Roux 2012) and Russia ( Pykälä et al. 2012). V. lignicola is apparently overlooked, but may also be rare.

Taxonomic notes: —According to the ITS phylogeny, the species belongs to V. hydrophila — a species usually growing on aquatic rocks. The high sequence variability of V. hydrophila specimens (similarity ranging from 94–100%) suggests that the species is actually a species group as already suspected by Orange (2013). Based on morphological and ecological differences, we prefer to treat V. lignicola as a species distinct from V. hydrophila , but further studies on the taxonomy of the V. hydrophila complex are needed. In V. hydrophila the involucrellum is more strongly diverging from the exciple, and the ascospores are larger. The mean length of the ascospores of V. hydrophila is 21.1 μm ( Orange 2013), which slightly exceeds the maximum length of V. lignicola ascospores measured in this study. The exciple of V. hydrophila is also larger (0.14–0.22 mm in diameter) ( Orange 2013) than the exciple of V. lignicola . Verrucaria lignicola also tends to have shorter periphysoids than V. hydrophila . In some specimens (including the type) the periphysoids are only 8–13 μm long, but other specimens include longer periphysoids (up to 20 μm long). The periphysoids of V. hydrophila are ca. 15–25 μm long.

Verrucaria hydrophila is an epilithic species, which is also rarely reported to be epiphytic ( Motiejűnaitë 2003). Epiphytic specimens of V. hydrophila have not been previously sequenced. Here we confirm an epiphytic occurrence of V. hydrophila . Our newly produced ITS sequence of the epiphytic specimen proved to be identical with the two sequences obtained from epilithic V. hydrophila specimens in GenBank.

The species may also be confused with V. corticola ( Arnold 1868: 959) Servít (1949: 21) , V. trabicola and V. rhizicola Aptroot & Thüs in Lumbsch et al. (2011: 112), which occur in similar habitats as V. lignicola . Verrucaria trabicola differs in larger perithecia and ascospores ( Lendemer & Breuss 2009). Verrucaria corticola and V. rhizicola differ in smaller ascospores: 12–15 × 5–6 μm.

Additional specimens examined: — FINLAND. Varsinais-Suomi: Lohja, Virkkala, Pähkinäniemi , shore forest of Lake Lohjanjärvi , on exposed roots of living Alnus glutinosa , 60°11’N, 23°58’E, 32 m a.s.l., 25.VII.2006, Pykälä 29141 ( H) ; Lohja, Vappula, Volssaari Island , shore of Lake Lohjanjärvi , deciduous forest, on exposed thick roots of Alnus glutinosa , 60°13’N, 23°57’E, 32 m a.s. l., 9.III.2007, Pykälä 30178 ( H) ; Karjalohja, Karkali, Karkali Strict Nature Reserve , stony shore of Lake Lohjanjärvi , exposed thick root of Alnus glutinosa , 60°14’N, 23°48’E, 32 m a.s.l., 5.X.2007, Pykälä 32067 ( H) ; Karjalohja, Karkali, Karkali Strict Nature Reserve , stony shore forest of Lake Lohjanjärvi , shore bank, on exposed root of a deciduous tree, 60°14’N, 23°47’E, 32 m a.s.l., 5.X.2007, Pykälä 32116 ( H) ; Karjalohja, Karkali, Karkali Strict Nature Reserve , shore forest of Lake Lohjanjärvi , stony shore, on exposed thick root of log of Alnus glutinosa , 60°14’N, 23°47’E, 32 m a.s.l., 6.X.2007, Pykälä 32143 ( H) .