A new vittarioid fern species, Haplopteris palustris, is here described from the swamp forests in western Malesia based on both morphological and molecular phylogenetic evidence. This species is unique among all recognized congeners with its strongly raised midrib on the adaxial lamina. Through phylogenetic analysis, it is resolved as the sister group of H. sessilifrons, a species usually found in lowland mixed dipterocarp forests. Additionally, we provide chromosome counts for this new species. Our finding underscores the significance of Southeastern Asian swamp forests, emphasizing the need for conservation endeavors and research to ensure the protection of this invaluable ecosystem.