WebSpecies: P. australis. Binomial name. Phragmites australis. ( Cav.) Trin. ex Steud. Synonyms. Arundo australis Cav. Phragmites australis, known as the common reed, is a species of flowering plant in the grass family Poaceae. It is a wetland grass that can grow up to 20 feet (6 metres) tall and has a cosmopolitan distribution worldwide.