The localization of psoromic acid and copper in partly green, copper-rich specimens of Lecidella bullata and Tephromela testaceoatra collected in Norway was studied by optical microscopy, scanning electron microscopy, and electron probe microanalysis. Infrared absorption spectroscopy of lichen material and of a synthetic copper-psoromic acid complex, and the other techniques, provide evidence that complexing of copper by psoromic acid occurs within specific areas of these lichens and this leads to their unusual colouration. In contrast, a specimen of copper-rich Lecanora cascadensis, which contains psoromic and usnic acids, does not contain such a complex. From the evidence obtained it is suggested that taxonomists should pay attention to the impact of rock and lichen chemistry on the appearance of lichen thalli.