Collemopsidium Nyl.,
Type : Collemopsidium iocarpum (Nyl.) Nyl. [=Pyrenopsis iocarpa Nyl.]
Description : Thallus crustose, immersed or superficial, usually gelatinous. Photobiont cyanobacterial, Gloeocapsa, Hyella or Nostoc. Ascomata perithecia, usually unilocular. Exciple dark-brown; wall ±cellular, generally heavily blackened; intercellular spaces in peridium normally melanised. Involucrellum generally lacking. Hamathecium of sparingly to richly branched and anastomosing pseudoparaphyses, septate, I−. Asci bitunicate with an apical beak, dehiscence fissitunicate, ovate to subcylindrical, usually with a long stalk, I−, 8-spored. Ascospores colourless, oblong to ovoid-fusiform, 1-septate, the upper cell generally shorter and broader than the lower; a poorly defined, gelatinous perispore occasionally present. Conidiomata pycnidia. Conidiogenous cells ±cylindrical, phialidic. Conidia bacillar to ellipsoidal.
Collemopsidium is a genus of some 14 described species, included in the Xanthopyreniaceae (Grube & Ryan 2002; Eriksson et al. 2004; Mohr et al. 2004; Pennycook & Galloway 2004; Eriksson 2005; Grube 2005). It is distinguished from Arthopyrenia by the ascomatal wall structure (in Arthopyrenia the ascomatal wall is hyphal containing bark cells, while in Collemopsidium the structure is ±cellular, without any substratum material); the absence of an involucrellum; the association with cyanobacterial rather than green algal photobionts; and the non-corticolous habitat preference (Harris 1975; Tucker & Harris 1980; Coppins 1988; 1992j – discussion in terms of Pyrenocollema; Grube & Hafellner 1990). Grube & Ryan (2002: 162) note "In recent works, Pyrenocollema Reinke has been used as a genus for the species treated here, but in the current concept, this is a highly heterogeneous assemblage of species. The type of the genus seems to be a parasite on Nostoc. It has thin, tangentially flattened cell walls at the outer layers of the peridium which are polygonal in surface view…The peridium of Collemopsidium is constructed differently: it is composed of irregularly shaped, interwoven cells (textura intricata)".
The majority of taxa occur on calcareous rock substrata, although recently a new terricolous species was described from Tasmania (McCarthy & Kantvilas 2000d). Nordin (2002) discusses the ecology and distribution of C. angermannicum in Sweden and gives useful information on the genus concept, and evolution and taxonomy of marine species in north-west Europe is reported by Mohr et al. (2004). One species is recorded from New Zealand where it is widespread on shells of marine animals (molluscs, cirripedes) on coastal rocks.
