Orthotrichum casasianum is a species of moss in the family Orthotrichaceae. It is endemic to the Spanish province of Álava, in the Basque Country.[2] It grows in less than 200 trees on the banks of the Bayas river.[3][4] The species is critically endangered, and was added in 2013 to the Basque Catalog of Threatened Species.[5]
^Mazimpaka, V.; Lara, F.; Garilleti, R.; Infante, M.; Heras, P. (1999). "Orthotrichum casasianum, a new epiphytic moss from humid forests of Northern Spain". Journal of Bryology. 21: 47–53. doi:10.1179/jbr.1999.21.1.47.