a seagrass species that is endemic to the Mediterranean Sea. It forms large underwater meadows that are an important part of the ecosystem. The flowering plant's common name is Neptune grass. In 2006 a huge clonal colony of P. oceanica was discovered south of the island of Ibiza. At 8 kilometres (5.0 mi) across, and estimated at around 100,000 years old, it may be one of the largest and oldest clonal colonies on Earth.