What is "prionium"

Prionium serratum, the palmiet, is a robust, evergreen, semiaquatic, rhizomatous flowering plant growing to in height. It is the only species in the genus Prionium, and is endemic to South Africa ( Cape Province and KwaZulu-Natal). Some authors have separated Prionium from the Thurniaceae, putting it instead in its own family, the Prioniaceae.