Porpidiaceae Porpidia platycarpoides Growth type crustose Chemical results: Medulla and apothecia margins K+ yellow > red, P+ yellow Frequently coastal on hard, well-lit siliceous rocks Pale greyish warted thallus with or without a black prothallus. Large apothecia to 3mm, discs often pruinose, with prominent smooth margins. Spores 15-23 x 7-10 µm. Microscope photograph below. Similar: Porpidia cinereoatra. Medulla K-, P-. Smaller spores P. macrocarpa. Medulla and margins of apothecia K+/- yellow, P+/- orange

Microscope photograph

Porpidia platycarpoides
Studland, Dorset. January and March 2013