a1 Botanical Museum, University of Oslo, Trondheimsveien 23 B, N-0562 Oslo 5, Norway
Rhizocarpon (subgenus Phaeothallus) santessonii sp. nov. is described from Norway. The species grows immersed in the areolae of Tremolecia atrata when young and later develops autonomous areolae. The species is further characterized by a yellowish grey thallus containing an unidentified pigment, a non-amyloidmedulla, and 1-septate spores which are persistently colourless or become unevenly brownwith age.
(Accepted April 25 1986)