Molecular Phylogeny of the Cliff Ferns (Woodsiaceae: Polypodiales) with a Proposed Infrageneric Classification

The cliff fern family Woodsiaceae has experienced frequent taxonomic changes at the familial and generic ranks since its establishment. The bulk of its species were placed in Woodsia, while Cheilanthopsis, Hymenocystis, Physematium, and Protowoodsia are segregates recognized by some authors. Phylogenetic relationships among the genera of Woodsiaceae remain unclear because of the extreme morphological diversity and inadequate taxon sampling in phylogenetic studies to date. In this study, we carry out comprehensive phylogenetic analyses of Woodsiaceae using molecular evidence from four chloroplast DNA markers (atpA, matK, rbcL and trnL–F) and covering over half the currently recognized species. Our results show three main clades in Woodsiaceae corresponding to Physematium (clade I), Cheilanthopsis–Protowoodsia (clade II) and Woodsia s.s. (clade III). In the interest of preserving monophyly and taxonomic stability, a broadly defined Woodsia including the other segregates is proposed, which is characterized by the distinctive indument and inferior indusia. Therefore, we present a new subgeneric classification of the redefined Woodsia based on phylogenetic and ancestral state reconstructions to better reflect the morphological variation, geographic distribution pattern, and evolutionary history of the genus. Our analyses of the cytological character evolution support multiple aneuploidy events that have resulted in the reduction of chromosome base number from 41 to 33, 37, 38, 39 and 40 during the evolutionary history of the cliff ferns.岩蕨科（Woodsiaceae）自建立以来，在科与属级分类阶元上经历了频繁的分类学修订。该科绝大多数物种曾被归入岩蕨属（Woodsia），而Cheilanthopsis、Hymenocystis、Physematium及Protowoodsia为部分学者所认可的分出属。由于该科类群形态多样性极高，且迄今的系统发育研究存在类群采样不足的问题，岩蕨科各属间的系统发育关系仍未明确。 本研究依托atpA、matK、rbcL及trnL–F共4个叶绿体DNA分子标记，对岩蕨科开展了全面的系统发育分析，涵盖了当前已确认物种的半数以上。结果显示，岩蕨科可划分为3个主要演化支，分别对应Physematium（演化支I）、Cheilanthopsis–Protowoodsia（演化支II）以及狭义岩蕨属（Woodsia s.s.，演化支III）。 为维持单系性与分类学稳定性，本研究提议采用广义岩蕨属的界定方案，将其余分出属并入该属，该广义类群以独特的毛被与下位囊群盖为典型鉴别特征。基于系统发育分析与祖先性状重建结果，本研究还对重新界定后的岩蕨属提出了全新的亚属分类系统，以更准确地反映该属的形态变异、地理分布格局与演化历史。 本研究对细胞学性状演化的分析表明，岩蕨类在演化历程中曾发生多次非整倍体事件，导致染色体基数从41逐步降低至33、37、38、39及40。