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Images of British Lichens

Caloplaca "citrina" auct. Brit., name misapplied
Caloplaca aff. austrocitrina Vondrák, Říha, Arup & Søchting

Thallus bright to chrome yellow, forming an irregular, areolate crust, areoles sorediate over much of their surface; apothecia with sorediate margins. Apparently common throughout Britain, including urban areas, on rocks, walls and other artificial substrates such as metal fences. Probably the commonest of a complex of species that includes C. limonia (page pending), C. arcis, C. dichroa (page pending) and C. flavocitrina.

Refs (for C. citrina, s.l., probably including C. aff. austrocitrina): Arup (2006) (photo); Wilk (2012), 23 (photo), 59-61; Smith et al. (2009), 259; Purvis et al. (1992), 149; Dobson (2011), 108 (photo); Jahns (1983), 246-247 (photo); Whelan (2011), 58 (photo); van Herk & Aptroot (2004, 2013), 90-1 (photo); Thomson (1997), 155; Lichen Atlas of the British Isles 6: 247 (2001).  N.B., the brighter orange taxon illustrated in Dobson (2005) under this name is C. dichroa, fide Fletcher & Laundon in Smith et al (op. cit.).

Refs. for C. austrocitrina: Vondrák et al. (2009), 587 (photo), 588; Wirth, Hauck & Schulz (2013), 1: 287, 294 (photo, but see below).

Recent work (see Powell & Vondrák (2011), British Lichen Society Bulletin 109: 25–27, and (2012), British Lichen Society Bulletin 110: 20–24) has shown that this widespread, typically chrome-yellow species that has been called "C. citrina" is not that species, and it is currently doubtful that true C. citrina occurs in Britain. The identity of British "citrina" is uncertain, but molecular work has shown it matches or is closely related to C. austrocitrina, recently described and known in central and eastern Europe. The photograph of C. austrocitrina in Wirth, Hauck & Schulz (2013) shows a Caloplaca with sorediate-margined apothecia, but the areoles are rather convex and sorediate initially at the margins.


If anyone can identify the millipede, please let me know.

Caloplaca citrina
Caloplaca citrina, closer view
millipede on Caloplaca citrina
Coastal rocks, Arbroath, Angus, April 2002

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Uploaded March 2008, last updated January 2016 (first hosted at, January 2003)