A new species of the Afro-Malagasy genus Phyllopentas Karehed & B. Bremer, Phyllopentas flava Razafim., T. Andriam. et Karehed, is described and illustrated. This plant is restricted to the Itremo region in southeastern Madagascar and is distinct morphologically from the other species of the genus by its pubescent, narrowly ovate to narrowly elliptic leaves, grey-whitish and thickly hairy midribs and secondary veins on the lower surfaces of leaves, and functionally dioecious and heterodistylous flowers. Summaries of distribution, phenology, habitat, and ecology are given and a conservation assessment is also provided.