Orthotrichum shawii Wilson, a distinct European species

Abstract

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