Taxonomy of Hedwigia filiformis (Bryopsida: Hedwigiaceae), with the clarification of the confounded identity of its synonym Hedwigia integrifolia

Background and Aims: Hedwigia integrifolia is still conflated with Hedwigidium imberbe, despite previous distinction of these two species. This paper offers clarification of the taxonomic status of Hedwigia integrifolia, as a synonym of H. filiformis. The latter name is re-established only for the species characterized by filamentous pseudoparaphyllia, leaf cells with peltate papillae, and perichaetial leaves ciliate. Methods: Protologues, specimens of Hedwigia worldwide from several herbaria, and personal collections were studied to evaluate the taxonomic and nomenclatural status of H. integrifolia, along with the similar species Hedwigia filiformis. Anatomical observations were recorded of pseudoparaphyllia, leaf cell papillae, and capsule neck stomata. Key results: My examination of numerous Hedwigia specimens worldwide led to the conclusion that Hedwigia integrifolia is a heterotypic synonym of Hedwigia filiformis. For the correct identification of Hedwigia filiformis, a morphological description and illustrations are provided for this species, so far known to occur in Canada, the USA, Mexico, Italy, Japan and South Korea.Conclusions: Hedwigia filiformis differs from other species in Hedwigia mostly by its slender sympodial branches, short ovate leaves with revolute margins, the very short hyaline leaf acumina, and the short elliptical apical cell.