Prostanthera marifolia, commonly known as Seaforth mintbush, is a critically endangered shrub which is endemic to New South Wales, Australia. The species was thought to be extinct until it was rediscovered in 2001.Prostanthera marifolia has an erect and open habit, growing to about 30 cm high. The leaves are ovate, but often appear triangular in outline due to recurved edges. They are 8 to 12 mm long and 4 to 6 mm wide.