Verrucaria margacea (Wahlenberg) Acharius

Schiavo, Lo, 2015, Revision of the Verrucaria elaeomelaena species complex and morphologically similar freshwater lichens (Verrucariaceae, Ascomycota), Phytotaxa 197 (3), pp. 161-185 : 182

Verrucaria margacea (Wahlenberg) Acharius ( Figs. 6D–E )

Flora Lappon.: 465 (1812) .— Thelotrema margaceum Wahlenb. In Ach., Methodus, Suppl. : 30–31 (1803); type: [ NORWAY, Finnmark, Alta] ad radicem alpis Konsamfjället [Komsa] loco humido, 3 May 1802, G. Wahlenberg. Holotype UPS!; epitype (designated here): NORWAY, Finnmark, Alta Commune, Alta , south side of Komsa , 69°58.88’N, 23°15.57’E, alt. 5 m, on wet rock on dripping bank near sea shore, unshaded, 1 July 2010, A. Orange 19155 (NMW - C.2010.001.124), GenBank accession no KM243204.

Prothallus absent. Thallus smooth to uneven (“bumpy”), usually distinctly cracked at least around the perithecia (but not in thin thalli), light to dark brown or greyish, thin 15–64 μm, not subgelatinous, in anatomical sections air filled spaces surrounding the hyphae in parts of the thallus visible. Photobiont cells 6–10 μm, irregularly arranged in the thallus, never in vertical columns. Perithecia forming distinct projections 465–675 μm, covered in a thin thallus mantle or upper part of involucrellum exposed, exciple 200–260 μm wide, periphyses 20–40 μm, asci pyriform to obovate 60–105 × 23–45 μm, ascospores (22.5) 27.7– 31.0 –34.2 (38.5) × (6.0) 11.3– 13.0 –14.8 (16.4) μm lenght/width ratio of ascospores (1.8) 2.1– 2.4 –2.7 (4.0) [170/13]. Halonate perispore generally absent. Pycnidia not observed.

Epitypification: The type of Thelotrema margaceum was collected by Wahlenberg in 1802, on irrigated rocks at the foot of a hill (now known as Komsa) by the town of Alta. The hill was visited in June 2010 by AO. Irrigated rocks were detected in only one place, and a small amount of material corresponding to the type material of T. margaceum was collected.

Habitat and distribution: Verrucaria margacea is a sub-aquatic species which grows on temporarily inundated rocks at and in streams, on lake margins and on wet rocks, where it occurs in both fully sun exposed and shaded localities. Specimens from shaded habitats have thinner thalli compared to those from sun exposed sites and the external morphology of very thin thalli of these shade forms can be similar to V. elaeomelaena agg. Sequenced specimens of this taxon have been seen from Norway, Iceland, Finland, Germany and Wales. Based on its morphology the species seems to be widespread in Scandinavia, including Iceland with scattered outposts across at high elevations in Central and Western Europe mountain ranges. This taxon is reported from arctic to temperate areas in both hemispheres (eg. Thomson 1997, Breuss in Nash et al. 2001) as well as from tropical mountain ranges eg. in India ( Singh & Sinha 2010) and Papua New Guinea ( Aptroot 1998). Genetic barcoding is required to confirm if all these populations are part of the Verrucaria margacea complex and how many species can be distinguished within this group.

? Syn.: Verrucaria leightonii Hepp

Flechten Europas 95. Syntypes BM!, W!, M!

Syntypes of Verrucaria leightonii are similar to V. margacea and all of them have elongated ascospores. The thallus surface is slightly smoother compared to the type of V. margacea but within the variation shown by other collections of V. margacea with near identical ITS sequences (eg. W0971, W1301). A confirmation of this taxon from the Alps requires sequenced material, but most of the historic collections of V. leightonii from this area fall in the morphological variation of V. margacea and we expect that this taxon will be verified when more sequences become available.

Figures

FIGURE 6. Habitus of European freshwater species of Verrucaria with large ascospores and spreading involucrellum. A. Holotype of Verrucaria basaltica (PRM). B. Holotype of Verrucaria pachyspora (PRM). C. Isotype of Verrucaria maasgeesterani (PRM). D. Specimen Thüs W Ice016 of Verrucaria margacea (BM). E. Isotype of Verrucaria margacea (W). Scale bar: A–E = 1 mm.