The twinsorus-fern genus Diplazium represents one of the most diverse genera within the lady-fern family Athyriaceae, encompassing over 300 species, with the highest species diversity concentrated in tropical Asia and the Neotropics. Despite recent progress in phylogenetic studies of Diplazium, the infrageneric classification of this fern group remains challenging, particularly in D. subg. Callipteris. In this study, we explored the phylogenetic relationships within Diplazium using plastid (plastome and amplicon sequences) and nuclear ribosomal data, based on an extensive species sampling. Our phylogenetic analyses, using plastid and nuclear ribosomal datasets, congruently support 4 major clades and 12 subclades. Although deep relationships along the backbone were consistently well resolved using plastomes, nuclear ribosomal genomes and three concatenated plastid markers, cyto-nuclear discordance was detected within subclades of D. subg. Callipteris. Considering our phylogenetic framework, we propose a classification of Diplazium with a particular focus on sectional delimitation. This classification comprises 4 previously recognized subgenera, and introduces 12 newly established sections. Our infrageneric divisions receive additional support from non-molecular evidence, including stipe scales, leaf architecture, pinna/pinnule shape, indument and venation patterns, sori and spore features, and geographical distributions.