Orthotrichum casasianum, a new epiphytic moss from humid forests of Northern Spain

A new epiphytic moss, Orthotrichum casasianum F. Lara, Garilleti & Mazimpak a, is described, which is characterized by leaves slightly flexuose when dr y, linear lanceolate or linear-oblong, with margins recurved and apices obt use to rounded, frequently concave and mucronate; upper cells with low papi llae or almost smooth; capsules emergent, uniformly brown, cylindric-urceol ate and strongly ribbed when dry except at base, stomata hemicryptoporous; exostome of 16 teeth fused into 8 pairs, reticulate on the external side an d almost smooth on the internal one; endostome of 16 linear, smooth and mar kedly incurved segments, calyptra naked. The new species is only known from two well preserved riparian woods in Northern Spain, beyond the Mediterran ean area. The new moss is taxonomically close to the complex group of holar ctic taxa related with O. scanicum Gronv., but is also similar to O. pallen s Brid. Characters discriminating the new moss from these species are discu ssed.