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Images of British Lichens

Caloplaca holocarpa (Hoffm.) A.E Wade

Thallus greyish to yellow or orange but usually poorly developed or almost absent, often as rather amorphous material just around the apothecia, soredia absent; apothecia dispersed to somewhat crowded, of mixed sizes, orange-yellow to deeper orange, thalline exciple scarcely developed but 'proper' margin relatively thick and conspicuous when young, much less visible as the apothecia mature and become convex. Often very common on sandstone and other siliceous rocks, on walls and on concrete, sometimes on mineral- or dust-impregnated wood.

Refs: Arup (2009), 120 & 121-3 (photos); Wilk (2012), 24 (photo), 70; Herk & Aptroot (2004, 2013), 99 (photo); Valcárcel et al. (2003), 143 (photo); Wirth, Hauck & Schulz (2013), 1: 282 (photo). The treatments in Smith et al. (2009), Lichen Atlas of the British Isles 6: 261 (2001), and other, generally older works must now be regarded as composite concepts. The identities of the photos in Dobson (2005, 2011) are maybe uncertain.

C. holocarpa was regarded as an uncertain and probably mixed concept until clarified by Arup (2009). He confirmed that there are indeed a group of morphologically very similar species, of which two are now known to be very common in the UK: true C. holocarpa, as described here, and C. oasis. The latter is often common on limestone and calcareous rocks and stonework, and on concrete wall-cappings where it often grows with C. holocarpa, but at least initially it frequently grows parasitically on Verrucaria species and colonies may remain centred on distinguishable remains. C. oasis generally has a more continuous, yellowish thallus and the apothecia tend to be more deeply red-orange, tightly clustered, rather uniform in size, with thinner proper margins that more quickly become indistinguishable from the apothecial discs. Measurements, including slight differences in the ascospores, are tabulated by Arup (page 115).


Caloplaca holocarpa
Caloplaca holocarpa, closer view
With Lecanora dispersa, Rinodina oleae, etc., on nutrient-enriched, sandstone wall of urban building, Paisley, Renfrewshire, September 2011.

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Uploaded September 2013, last updated January 2016