Candelariella coralliza (images of British lichens)

Thallus thick, cracked-areolate, of densely aggregated, spherical, yellow granules; apothecia yellow, rare. Widespread but more frequent in the north and west, often as isolated colonies on nutrient-enriched rocks and stonework used as bird perches, such as the highest point along a dry-stone wall. (One local site is on an ancient, ornamental sundial that birds use as a vantage point in the middle of a formal garden.)
Refs: Smith et al. (2009), 277; Purvis et al. (1992), 161; Dobson (2005), 111 (photo); Jahns (1983), 210-11 (photo); Wirth (1995), 1: 243 (photo); Moberg & Holmåson (1984), 132 (photo); Thomson (1997), 181, 183 (photo).

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Alan Silverside's Lichen Pages