Umbilicaria platyrhiza Davydov sp. nov. is described within the Umbilicaria crustulosa – U. spodochroa species complex and illustrated. The new species resembles Umbilicaria crustulosa phenotypically, but is distinct by apothecia with a single gyrus of sterile tissue, grey-brown to black lower surface with flattened to strap-like rhizinomorphs, and by producing umbilicaric (vs. crustinic) acid. Umbilicaria platyrhiza inhabits silicate rocks at low elevations in the Mediterranean region of Eurasia (Prov. Izmir in Turkey and Burgas Region in Bulgaria). Keywords: Asia, endemic, Europe, HPLC, lichens, new taxa, U. vellea-group.