A new pteridophyte species, Polystichum manickamianum Benniamin, Fraser-Jenkins & Irudayaraj, is described and illustrated from the Agasthiar Hills, South Western Ghats, South India. It is a member of Polystichum Roth sect. Macropolystichum Daigobo (Dryopteridaceae) and is distinguished from its nearest relatives by its relatively short, wide fronds with large, ovate-rhombic, crenate, dark green pinnules with submarginal sori, sparsely hairy upper stipe, rachis, and costae, and by the absence of subapical proliferous bulbils on the rachis. It is endemic to Tamil Nadu, South India, and is considered to be Critically Endangered (CR) based on IUCN Red List criteria. A key is provided to South Indian Polystichum, and some problematic related names are discussed. A lectotype is designated for Aspidium tacticopterum Kunze. Polystichum kunthianum B. K. Nayar & Geevarghese is newly synonymized into P. subinerme (Kunze) Fraser-Jenkins.