Periyar is rich in medicinal plants. More than 350 species have been recognised as medicinally important. Majority of the medicinal plants are trees followed by herbs and shrubs. Among the families with species of medicinal importance, Fabaceae comes first followed by Euphorbiaceae. The evergreen forests support the majority of the medicinal plants followed by moist deciduous forests and southern hilltop tropical evergreen forests.
The common species are Glory Lily, (Gloriosa superba), Kino Tree (Pterocarpus marsupium), Gymnema sylvestre, Hemidesmus indicus etc. Begonia albo-coccinea is categorisd as vulnerable.