A new species of the Sempervivum marmoreum group in Central Europe.

A comparative study of material of Sempervivum marmoreum Griseb. from the type locality (Mt Athos, Greece) and the northern part of its distribution revealed a distinct morphotype occurring in an isolated enclave along the Slovak–Hungarian border. As its karyotype differs it is formally described here as a new species – Sempervivum matricum Letz. The name Sempervivum assimile Schott, formerly considered as a possible name for this species is here critically examined. A morphological characterization of the new species, photographs of the plant and a distribution map based on revised herbarium specimens are provided.