A crustose species with a brownish grey to chocolate brown thallus that has a hint of purple. The thallus is areolate-cracked, often with a fimbriate brown-black prothallus. The apothecia are innate, flat and black, with an inner margin that is paler on the inner edge.
Medulla: C+- red, K+- yellow
Rhizocarpon richardii is widespread along the Scottish coast where it grows on siliceous rocks and pebbles or stable shingle in the xeric-supralittoral zone. BLS distribution map
scottishlichens.co.uk 