Images of British Lichens
Rhizocarpon umbilicatum (Ramond) Flagey
Thallus matt, rather thick, chalky white, pruinose, usually cracked-areolate; apothecia inially set into the thallus surface, flat, black with grey-pruinose rims; closely similar to R. petraeum but with a slightly thicker thallus and apothecia not or only indistinctly arranged in concentric circles, differing microscopically in its smaller ascospores. On calcareous rock, generally hard limestones, including in churchyards, widespread but local.
Refs: Smith et al. (2009), 808; Purvis et al. (1992), 541; Dobson (2005), 390 (photo); Dobson (2011), 394 (photo); Jahns (1983), 207 (photo), 208; Wirth, Hauck & Schulz (2013), 2: 987, 997 (photo); Holien & Tønsberg (2008), 188 (photo); Puntillo (1996), plate 35 (photo, but apothecial discs shown as pruinose); Thomson (1997), 552.
Compare Solenopsora candicans, which can be superficially similar but in which the apothecia have defined, white, thalline margins.
|On limestone outcrop, near Arncliffe, Yorkshire, June 2009|
|On calcareous stonework, Islay, May 2011 (BLS meeting, material lent by Mark Powell)|
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Uploaded September 2012, updated September 2013