Images of British Lichens
Collemopsidium foveolatum (A.L. Sm.) F. Mohr
(= Pyrenocollema halodytes auct., in part)
Description based on Mohr et al. (2004): thallus immersed; perithecia 0.10–0.24 mm. diameter, black, flattened to moderately convex, immersed in pits in shells and softer rocks. Common on rocky shores, on chalk, limestone or on shells of molluscs and barnacles, evidently contributing to weakening and erosion of shells as indicated in the photograph below.
Refs: Mohr et al. (2004), 528 (photo), 529; Orange (2008), 45 (line illustration); Smith et al. (2009), 359; Dobson (2005), 377 (photo only; text description acknowledged as covering both C. faveolatum and C. halodytes, under Pyrenocollema); Dobson (2011), 162 (photo); Jahns (1983), 260-261 (photo, as Arthopyrenia halodytes); Moberg & Holmåson (1984), 219 (photo, as "Arthropyrenia sublitoralis"); Puntillo (1996), plate 34 (photo, as P. halodytes); Hansen & Anderson (1995), 111 (photo, as P. halodytes).
Mohr et al. (2004) presented compelling evidence that the much used name, Pyrenocollema halodytes, included at least three well defined species, differing in morphology and ecology, and clearly demarked by DNA sequencing. The familiar species on shells and barnacles is NOT P. halodytes, and all now belong in the genus Collemopsidium. True Collemopsidium halodytes has a thin, brownish, surface thallus with the perithecia less immersed in the substratum, and occurs generally on base-poor maritime rocks. It is evidently described and illustrated (as Pyrenocollema) in van Herk & Aptroot (2004), pp. 330-1.
Note that C. sublitorale, with much larger, less immersed perithecia, also occurs on shells and barnacles.
|In shell of acorn barnacle (? Chthamalus montagui, but badly eroded), Kennedy's Pass, Ayrshire, May 2008|
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© A.J. Silverside
First uploaded (as Pyrenocollema halodytes), September 2008, revised February 2009, last modified June 2012