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Page number:600 
Remarks (internal):Recognized by the rather large perithecia and large, when mature dark brown spores. A variable species usually having a pale grey, thick, almost bullate thallus with minutely uneven verrucae appearing pruinose or sometimes with a rimose thallus with rather flattened areolae. The perithecia are usually irregularly covered by lobe-like extensions from the thallus.
Verrucaria subpyrenophora Leight. The spores of the Leigthon material studied by us are rather small for S. schaererianum, but we still think it is within the range of variation of this species. However, a careful study of the local population in Wales should be undertaken. Sommerfelt when describing Verrucaria theleodes was studying material belonging to two species, and the protologue refers to features of them both; ? contigua belonging to S. schaererianum, but the lectotype of Verrucaria theleodes actually belongs to a another genus dealt with in a different context (Savi? & Tibell, submitted). The lichenicolous ascomycete Stigmidium superpositum (Nyl.) D. Hawksw., previously only known from S. terrestre, was in one case found growing on S. schaererianum.
Description type:Non-original description 
Description:S. schaererianum A. Massal. = Verrucaria theleodes ? contigua Sommerf., Suppl. fl. lapp.: 140. 1826: 'Hab. in rupibes interdum stillicidiis irrigatis per Nordlandiam saltensem ex. gr. Ad Fiskevaagsosen Saltdalen copiosae' - Type: 'Verrucaria theleodes ? contigua Smrf. Suppl. Saltdalen. Sommerfelt.' in Th.M. Fries' hand (lectotype, designated here, UPS). = Verrucaria subpyrenophora Leight. - Original material: 'V. subpyrenophora Leight. Cwm Cywion' (UPS!).
Thallus superficial, moderately thick to thick, grey to pale grey, verrucose; verrucae when young almost spherical, 0.4-0.8 mm diam., later irregularly elongated and aggregated with other verrucae, forming lobe-like extensions (Fig. 5E); thalline surface minutely areolate or appearing pruinose; Photobiont cells in radiating rows. Cephalodia frequent, almost dark brown to black, forming flattened, irregular, granular aggregations up to 1.5 mm diam. Perithecia formed from the bases of the thalline verrucae, but later usually irregularly encroached by thick lobe-like thalline projections, sometimes, however, the thalline cover is very poorly developed or missing; rather large, 0.68-0.85 mm diam. (X = 0.76 mm, sd = 0.085 mm, N = 9, n = 55), spherical; exposed outer surface of the involucrellum uneven; involucrellum 55-130 ?m thick, strongly thickened around the often distinctly depressed ostiolum, in the upper part merged with the excipulum; pseudoparaphyses numerous. Hymenium I+ red, KI+ blue. Asci 130-236 x 57-92 ?m, ellipsoidal to clavate, 8-spored. Ascospores 59-73 x 31-39 ?m (X = 66.2 ?m, sd = 6.8 ?m, N = 36; n = 138; X = 35.2 ?m, sd = 4.1 ?m, N = 36; n = 138) ellipsoidal or often somewhat asymmetric, slightly curved with one end being somewhat wider, sometimes ovoid, when dark brown, muriform (Fig. 6D). At high magnification a very minute dotted pattern in the spore wall is visible under the light microscope. This might be caused by a surface ornamentation or irregular distribution of a pigment. Photobiont: trebouxioid, in the cephalodia Nostoc sp.
Ecology and distribution. - On calcareous rocks and on slate, along rivers and in the mist of waterfalls; montane but also occurring at low elevations in the northernmost part of Scandinavia and the Arctic. Altitudinal range: 10-1,170 m. Originally described from Switzerland, but also known from Northern Finland, Central and Northern Sweden, and Greenland. It further occurs in the British Isles (Swinscow, 1971), from other areas in Central Europe (see e.g., V?zda & Liška, 1999; Hafellner & Türk, 2001; Clerc, 2004 for further references), and the American Arctic (Thomson, 1997).

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