» Pos(e)idonia also refers to the city of Magna Graecia later known as Paestum Posidonia is a genus of flowering plants. It contains two to nine species of marine plants ("seagrass"), found in the seas of the Mediterranean and around the south coast of Australia. The APG system (1998) and APG II system (2003) accept this genus as constituting the sole genus in the family Posidoniaceae, which it places in the order Alismatales, in the clade monocots. The AP-Website concludes that the three fami… (More on Posidoniaceae)