Verrucaria vacillans Pykaelae & Myllys, 2020

Pykaelae, Juha, Kantelinen, Annina & Myllys, Leena, 2020, Taxonomy of Verrucaria species characterised by large spores, perithecia leaving pits in the rock and a pale thin thallus in Finland, MycoKeys 72, pp. 43-92 : 43

Verrucaria vacillans Pykaelae & Myllys sp. nov. Fig. 2G

Diagnosis.

Species characterised by dark lines between contiguous conspecific thalli, pale usually endolithic thallus, perithecia leaving shallow to deep pits in the rock, very variable involucrellum, ascospores (18-)23-28(-32) × (8-)11-13(-15) mm, morphologically rather similar to the Finnish species of the V. subtilis complex, but the sequence divergence in ITS 4.5-6.8%.

Holotype.

Finland. Enontekiön Lappi, Enontekiö, Porojärvet, Toskalharji, Toskalpahta, fell, SW-slope, scree, on dolomite boulder, 795 m alt., 69°11'N, 21°29'E, 1 Aug 2011, J. Pykälä 43118 (H9205851, GenBank accession number: MT229829).

Description.

Prothallus absent. Thallus white, whitish grey or pale brownish, mainly endolithic to thinly epilithic, 20-170 mm thick, algal cells 5-10 mm, contiguous conspecific thalli separated by dark lines, 0.21-0.41 mm wide. Perithecia 0.15-0.47 mm in diam., 1/4-3/4-immersed, usually leaving shallow to fairly deep pits in the rock, rarely few perithecia not leaving pits, often surrounded by a thalline collar, 60-160(-200) perithecia/cm2. Ostiole tiny or conspicuous, pale to dark, plane or depressed, ca. 20-40(-60) mm wide, wider ostiolar depression occasionally present, up to 160 mm wide. Involucrellum apical, covering half of the exciple, exceeding half of the exciple or rarely to the exciple base, 30-70(-90) mm thick, appressed to the exciple, moderately diverging from the exciple, strongly diverging from the exciple or even spreading outwards away from the exciple. Exciple 0.15-0.26 mm, wall dark brown or black, 17-35 mm thick. Periphysoids ca. 25-40(-50) × 1.5-2.5 mm, branching. Asci 67-84 × 27-28 mm, 8-spored. Ascospores 0-septate, (18.1-)22.7-25.3-28.0(-31.7) × (8.3-)10.8-11.9-13.1(-15.2) mm (n = 228), perispore 1-1.5 mm thick.

Habitat and distribution.

The species is restricted in Finland to the calcareous mountains (Scandes) in NW Finland above the tree level. It always grows on dolomite. It grows on rock outcrops, boulders, stones and pebbles.

Etymology.

The specific epithet refers to the high morphological variation in the involucrellum from apical to (rarely) reaching the exciple base level, from being appressed to the exciple to spreading outwards away from the exciple and from fairly thin to thick.

Other specimens examined.

Finland. Enontekiön Lappi, Enontekiö, Porojärvet, Toskalharji, Toskalpahta, fell, SW-slope, scree, on dolomite pebbles, 785 m alt., 69°11'N, 21°29'E, 1 Aug 2011, J. Pykälä 43058 (H); Enontekiö, Porojärvet, Toskalharji, Toskaljärvi N, fell, gentle SE-slope, dolomite rock outcrop, on dolomite stones, with V. foveolata , 730 m alt., 69°12'N, 21°26'E, 2 Aug 2011, J. Pykälä 43232 (H); Enontekiö, Porojärvet, Toskalharji, Toskaljärvi N, fell, dolomite rock, gentle S-slope, on dolomite stone, 720 m alt., 69°12'N, 21°26'E, 2 Aug 2011, J. Pykälä 43272 (H); Enontekiö, Porojärvet, Toskalharji, Toskaljärvi N, fell, dolomite rock, on SE-facing wall, 720 m alt., 69°12'N, 21°26'E, 2 Aug 2011, J. Pykälä 43296 (H); Enontekiö, Porojärvet, Toskalharji, Toskaljärvi N, fell, dolomite rock, gentle SE-slope, on dolomite pebbles, 730 m alt., 69°12'N, 21°26'E, 2 Aug 2011, J. Pykälä 43302 (H); Enontekiö, Porojärvet, Toskalharji, Toskaljärvi N, fell, dolomite scree, on dolomite boulder, rather abundant, 710 m alt., 69°11'N, 21°26'E, 2 Aug 2011, J. Pykälä 43384 (H); Enontekiö, Kilpisjärvi, Saana, nature reserve, E-part, fell, dolomite rock, on SW-facing wall, 880 m alt., 69°02'N, 20°51'E, 10 Aug 2011, J. Pykälä 44075, 44081b (H); Enontekiö, Kilpisjärvi, Saana, fell, steep NE-slope, dolomite rock, on NE-facing wall, 820 m alt., 69°02'N, 20°51'E, 11 Aug 2011, J. Pykälä 44142, 44162 (H); Enontekiö, Kilpisjärvi, Saana, nature reserve, E-part, fell, steep SW-slope, dolomite rock, on SW-facing wall, 730 m alt., 69°02'N, 20°51'E, 12 Aug 2011, J. Pykälä 44255 (H).

Notes.

Based on ITS sequences, V. vacillans is genetically well distinct from other Verrucaria species. However, it may be confused with several other species. Verrucaria vacillans is most difficult to separate from V. cavernarum , V. difficilis and V. subtilis . In these three species, dark lines between contiguous conspecific thalli are never present. Verrucaria cavernarum and V. subtilis have an involucrellum seldom exceeding half of the exciple (and then only in a minority of perithecia). The exciple of V. subtilis is sometimes pale (although usually dark). The spores tend to be slightly broader in V. vacillans than in V. subtilis . However, specimens of V. vacillans without dark lines and with a short involucrellum may not be possible to separate from V. cavernarum and V. subtilis by morphology. Specimens of V. vacillans with a deep reaching involucrellum may not be separable from V. difficilis if dark lines are absent. Verrucaria vacillans may also be confused with V. devergens , V. kuusamoensis , V. epilithea and V. muralis . Verrucaria kuusamoensis has an involucrellum usually exceeding half of the exciple, larger spores and dark lines are rather rare. Verrucaria devergens has larger spores and the involucrellum is usually absent or sometimes apical. Verrucaria epilithea and V. muralis have perithecia not leaving pits or the pits are shallow, the spores do not exceed 26 mm in length and dark lines are absent.

Names considered inapplicable to the species treated above

Figures

Figure 2. Habitus of the new Verrucaria species A V. bifurcata (holotype) B V. cavernarum (holotype) C V. difficilis (holotype) D V. fuscozonata (holotype) E V. kuusamoensis (holotype) F V. subdevergens (holotype) G V. vacillans (holotype). Scale bars: 1 mm (A-D), 0.5 mm (E-G).