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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.

Rhizocarpon umbilicatum
Rhizocarpon umbilicatum
On limestone outcrop, near Arncliffe, Yorkshire, June 2009
Rhizocarpon umbilicatum
On calcareous stonework, Islay, May 2011 (BLS meeting, material lent by Mark Powell)

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© A.J. Silverside
Uploaded September 2012, updated September 2013