Description and phylogenetic investigation of <i>Pogonatum shevockii</i> 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.本文记述产自中国台湾的新种谢瓦克小金发藓（Pogonatum shevockii），该种具备多项独特形态特征。仅采自云南的一号标本被归为该种，但仍需进一步采样以确认其与台湾材料在形态及分子层面的差异是否足够稳定，从而具备分类学上的独立认定价值。该种藓类具有独特的叶部结构：叶层由3层细胞构成，其中央具一列大型透明细胞，这一结构可能是导致叶背在干燥时呈现显著淡灰蓝色的原因。此类透明细胞常含有球状内含物，根据放大倍率的不同，内含物可呈现深色、或具黄褐色/蓝绿色斑点的外观。台湾标本的新鲜材料中，蒴帽毛通常呈鲜明绿色，这是金发藓科（Polytrichaceae）中少见的特征。本研究涵盖75%小金发藓属（Pogonatum）物种的代表类群进行分子系统发育分析，结果强力支持该新分类单元为单系群，并初步将其置于与一个包含5个物种的支系互为姊妹群的位置。该5物种均具成对顶端板状细胞，分别为仅分布于中美洲及南美洲的P. campylocarpum、P. neglectum、P. comosum和P. procerum，以及分布于亚洲的P. microstomum。