Taxonomic Revision of the Asiatic Widespread Filmy Fern Cephalomanes javanicum (Hymenophyllaceae, Polypodiidae) Reveals More Species than Expected

This study revises the taxonomy of <i>Cephalomanes javanicum</i> (Hymenophyllaceae), a filmy fern traditionally considered widespread across the Indomalayan and Australasian regions. Through a comprehensive analysis of the literature, type specimens, and herbarium collections, we clarify the taxonomic status of three recognized varieties: typical <i>C. javanicum</i>, <i>C. javanicum</i> var. <i>sumatranum</i>, and <i>C. javanicum</i> var. <i>asplenioides</i>. Morphological, morphometric, and molecular phylogenetic investigations reveal that these varieties represent distinct species rather than intraspecific variants. Additionally, we reassess <i>C. atrovirens</i>, a species often confused with <i>C. javanicum</i>, and confirm that its two previously recognized subspecies also warrant species status. Based on these findings, we propose the elevation of the <i>C. javanicum</i> varieties and <i>C. atrovirens</i> subspecies to full species rank, providing updated taxonomic treatments, synonymy lists, and new lectotypifications. These revisions contribute to a more accurate understanding of species diversity within <i>Cephalomanes</i> and have broader implications for fern taxonomy, biogeography, and conservation in the tropical Asia, Australasian, and Oceanian regions.