Orthotrichum shawii Wilson, a distinct European species

During the last three decades, Orthotrichum shawii Wilson has been consider ed to be conspecific with O. striatum Hedw. The discovery of new population s of this moss in Southern Europe (N. W. Iberian Peninsula and Sicily) afte r more than seventy years allowed the re-evaluation of its taxonomical stat us and relationships. It is concluded that O. shawii is a distinct species, easily distinguished from related species by sporophytic characters: capsu le scarcely or not ribbed, exostome of 16 whitish and opaque teeth recurved to the theca when dry, and endostome absent or consisting of eight vestigi al segments; additionally, the areolation of the exothecium cells as well a s the peristome ornamentation represent significant differences from O. str iatum Hedw. that support the specific status of this moss. It is redescribe d and keys for its discrimination from closely related species as well as i nformation on its ecology and distribution are provided.