Verrucaria devergens Nyl., Flora 55: 362, 1872 (as V. divergens Nyl., a typographic error)

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 devergens Nyl., Flora 55: 362, 1872 (as V. divergens Nyl., a typographic error)

Type.

[Russia,] Suojärvi, ad saxa calcarea Pöpönsaari, 1870, Norrlin (H!, H-NYL 3036a!, syntypes).

Description.

Prothallus absent. Thallus white, grey or pale brown, endolithic, rarely epilithic (two sequenced specimens), thin, continuous, algal cells 5-8 mm, occasionally (three sequenced specimens) contiguous conspecific thalli separated by dark brown lines, 0.13-0.22 mm wide. Perithecia 0.13-0.40 mm in diam., (1/4-)1/2-1-immersed, leaving shallow to deep pits in the rock, few perithecia occasionally not leaving pits, often surrounded by a thalline collar, sometimes thinly thalline covered; 50-140 perithecia/cm2. Ostiole usually inconspicuous, pale or dark, plane or depressed, ca. 20-50 mm wide. Involucrellum absent or apical, short, rarely covering half of the exciple (two sequenced specimens), (40-)50-80 mm thick, appressed to the exciple or diverging from the exciple. Exciple 0.20-0.35 mm in diam., wall dark brown or black, ca. 27-40 mm thick, apex thickened to ca. 50-100 mm thick if the involucrellum is absent. Periphysoids ca. 30-50(-60) × 1-2.5 mm, branching or branched-anastomosing. Ascospores 0-septate, (20.2-)24.6-27.4-30.2(-34.8) × (10.2-)11.7-12.6-13.5(-15.7) mm (n = 281), perispore 1 mm thick.

Habitat and distribution.

The species is a strict calcicole occurring on calcareous rocks. It may prefer fairly humid habitats. Verrucaria devergens seems to be able to tolerate moderate flooding and it also grows on subaquatic calcareous rocks on river shores in the Oulanka area. It is not rare on dolomite rocks in the Oulanka and Kilpisjärvi areas in northern Finland, but seems to be absent from southern Finland.

Other specimens examined.

Finland. Koillismaa, Kuusamo, Oulanka National Park, Pikkukönkäänkuru, Pinus sylvestris -dominated forest, SW-slope, on dolomite stones, 178 m alt., 66°21'N, 29°19'E, 8 Aug 2009, J. Pykälä 35922 (H); Kuusamo, Oulanka National Park, Pikkukönkäänkuru, dolomite rock crop, on overhanging SW-facing wall, 173 m alt., 66°21'N, 29°19'E, 8 Aug 2009, J. Pykälä 35933 (H); Kuusamo, Oulanka National Park, Pikkuköngäs, N shore of river Oulankajoki, dolomite rock outcrop, on SW-facing wall, 160 m alt., 66°22'N, 29°19'E, 12 Aug 2009, J. Pykälä 36220 (H), 36244 (H), 36245 (H); Kuusamo, Oulanka National Park, Pikkuköngäs, N shore of river Oulankajoki, dolomite rock outcrop, stony shore, on stones, 160 m alt., 66°22'N, 29°19'E, 12 Aug 2009, J. Pykälä 36234 (H); Kuusamo, Oulanka National Park, Pikkuköngäs, N shore of river Oulankajoki, dolomite rock outcrop, on 1 m high SW-facing wall, 160 m alt. 66°22'N, 29°19'E, 12.VIII.2009, J. Pykälä 36271 (H); Kuusamo, Oulanka National Park, Kiutaköngäs, N shore of river Oulankajoki, dolomite rock outcrop, on SE-slope, 150 m alt., 66°22'N, 29°20'E, 12 Aug 2009, J. Pykälä 36304 (H); Kuusamo, Oulanka National Park, Kiutaköngäs, by the rapids, S shore of Oulankajoki river, calciferous (dolomite) schistose rock outcrop, NE-slope, on E-facing wall, 152 m alt., 66°22'N, 29°19'E, 13 Aug 2010, J. Pykälä 39898 (H); Kuusamo, Oulanka National Park, Kiutaköngäs, by the rapids, S shore of Oulankajoki river, calciferous (dolomite) schistose rock outcrop, on gentle NE-slope, 152 m alt., 66°22'N, 29°19'E, 13 Aug 2010, J. Pykälä 39901 (H); Kuusamo, Oulanka National Park, Taivalköngäs, shore of Oulankajoki river, stony river shore, on dolomite stone, 170 m alt., 66°24'N, 29°11'E, 25 Aug 2011, J. Pykälä 45090 (H); Kuusamo, Oulanka National Park, Mataraniemi W, shore of Oulankajoki river, small dolomite rock outcrop, on 40 cm high SE-facing wall, 145 m alt., 66°22'N, 29°20'E, 28 Aug 2011, J. Pykälä 45367 (H); Salla, Oulanka National Park, 400 m N of Savilampi, shore of river Savinajoki, cliff, dolomite rock outcrop, on overhanging NE-facing wall, 177 m alt. 66°25'N, 29°10'E, 13 Aug 2009, J. Pykälä 36344 (H); Salla, Oulanka National Park, Savilampi 1.4 km NE, shore of Savinajoki river, dolomite rock outcrop, SE-slope, on dolomite boulder, 184 m alt., 66°26'N, 29°11'E, 23 Aug 2011, J. Pykälä 44914 (H); Enontekiön Lappi, Enontekiö, Porojärvet, Toskalharji, Toskaljärvi N, fell, gentle SW-slope, dolomite scree, on dolomite boulders, 710 m alt., 69°11'N, 21°26'E, 3 Aug 2011, J. Pykälä 43421 (H); Enontekiö, Kilpisjärvi, Saana, nature reserve, E-part, fell, dolomite rock outcrop, on SW-facing wall, 880 m alt., 69°02'N, 20°50'E, 10 Aug 2011, J. Pykälä 44042 (H).

Notes.

Based on the ITS phylogeny, V. devergens , V. karelica and V. subdevergens are very closely related. They are here considered as distinct species, based on the ITS phylogeny and because of a barcoding gap between the species. Verrucaria devergens is morphologically more variable than previously known ( Pykälä 2007). Usually, the species has no involucrellum, but the apex of the exciple is thickened. However, specimens with an apical involucrellum, as well as two specimens in which the involucrellum covers half of the exciple, have an identical ITS sequence compared to the typical V. devergens . Typically, V. devergens has perithecia varying from half-immersed to immersed in the same specimen, but in some specimens, the perithecia are 3/4-1-immersed, while in a few others, they are 1/4-1/2-immersed.

Verrucaria devergens is difficult to separate from V. foveolata , V. karelica and V. subdevergens . V. devergens and V. foveolata show similar variation in the involucrellum, i.e. absent or apical. Verrucaria foveolata has larger spores, but there is a wide overlap in the spore size. Verrucaria foveolata usually has immersed perithecia, while V. devergens has 1/2-1-immersed perithecia. However, some specimens of V. devergens are similar to V. foveolata in having 3/4-1-immersed perithecia. No consistent morphological differences were found between V. devergens and V. karelica , although all specimens of V. karelica have an involucrellum. Verrucaria karelica may have more often an epilithic thallus and dark lines between contiguous conspecific thalli. Verrucaria subdevergens has a longer involucrellum than V. devergens in all studied specimens predominantly exceeding half of the exciple.

Specimens of V. devergens with untypically deep reaching involucrellum may be difficult to separate from V. kuusamoensis and V. subtilis . Verrucaria kuusamoensis tend to have a smaller exciple and shorter periphysoids, the thallus is usually epilithic and the involucrellum usually exceeds half of the exciple. Verrucaria subtilis has thinner and smaller exciple and, on average, smaller spores. In some specimens of V. subtilis , pale exciples are present, while they have never been found from V. devergens .