The stalkless, opposite leaves of Penaea mucronata spread, spaced and veering sufficiently away from the pale stems to expose hairy stem parts. Broad at the base, the heart-shaped leaf tapers to an acute tip, its pale margins curling up slightly.

Both the bracts spreading below the flowers and the lobes of the cylindrical floral tubes are pointed. The stamens are about as long as the floral tubes, the anthers longer than the filaments. The ovary has four locules (Manning, 2007; Leistner, (Ed.), 2000).