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(Map updated: 11 August 2009)

The thallus of this small, Porpidioid crustose lichen is immersed. Discs are black, scattered and unfrosted, in shallow pits in limestone or calcareous rocks, often forming higgledy-piggledy lines along crevices. It is easily confused, in the natural limestone heartlands such as the Burren, with C. chondrodes which is similar. However, that species has crowded discs and smaller spores (excluding perispore) 13-18ųm long, compared with spores 16-20ųm long, in C. metzleri. In Ireland, it occurs mainly in the west where some past records may be those of C. chondrodes.

Key characteristics

• Thallus immersed; discs black, non-pruinose, dispersed, in shallow pits
• On calcareous rocks, the discs often running along the crevices like a sprinkling of footprints.

Original text submitted by Vince J. Giavarini