Description and phylogenetic investigation of Pogonatum shevockii N.E.Bell & Hyvönen (Polytrichaceae), a new East Asian species with a unique leaf morphology

We describe Pogonatum shevockii from Taiwan, a new species with a number of unusual features. A single collection from Yunnan is treated as conspecific, although further sampling is required to confirm whether morphological and molecular differences from the Taiwanese material are sufficiently consistent to be recognised taxonomically. The plants have a remarkable leaf structure with a 3-stratose lamina including a central row of large hyaline cells that may be responsible for the abaxial surfaces of leaves appearing distinctly pale-glaucous when dry. These cells often have globular inclusions that appear variously dark or speckled yellow-brown/blue-green depending on magnification. In fresh material of Taiwanese specimens the calyptra hairs are often distinctly green, another unusual feature in the Polytrichaceae. Molecular phylogenetic analyses including exemplars from 75% of Pogonatum species strongly support the monophyly of the new taxon and tentatively place it as sister to a clade including five species with geminate apical lamellar cells, namely the exclusively Central and Southern American P. campylocarpum, P. neglectum, P. comosum and P. procerum and the Asian P. microstomum.