On Rhizocarpon obscuratum (Ach.) Massal., with notes on some related species in the British Isles

The specimens upon which Lecidea petraea var, obscurata Ach., the basionym of Rhizocarpon obscuratum (Ach.) Massal., is based are shown to be mostly referable to the species currently known as R. lavatum (Fr.) Hazslin. Rhizocarpon reductum Th. Fr. is resurrected to accommodate specimens with small ascospores previously referred there. The related species R. sublavatum is described from the Scottish Highlands and descriptions provided for R. anaperum (Vain.) Vain. and R. amphibium (Fr.) Th. Fr. These species are compared with R. reductum, R. lavatum and R. petraeum. Rhizocarpon rubescens Th. Fr. is shown to be a distinct species recorded from Europe and N. America. (C) 2000 The British Lichen Society.