The discovery of a Tornabea in California and Mexico brought the authors to critically compare the two currently accepted species of the genus, T. scutellifera (Old World) and T. ephebea (South America), based on the anatomical and morphological analysis of 98 samples. The results show that the morpho-anatomy of T. ephebea lies within the range of variation of the highly polymorphic T. scutellifera. The two taxa are conspecific and the former name is consequently a synonym of the latter. The species is new to the U.S. and Mexico. A distribution map based on specimens studied and on literature records is presented; T. scutellifera has a broad, but disjunct distribution in semi-arid areas with frequent periods of high air humidity, including Europe (with a Mediterranean-Atlantic range), North Africa, southwestern Asia, California, Mexico, western Chile, and Peru. The species is often associated with a member of the Teloschistes villosus complex - T. villosus s. str. in the Old World and T. californicus in the New World. The latter species is reported as new to South America (Chile).