Plants are multicellular, photosynthetic eukaryotes that form their own kingdom, Plantae.
The only living species that can manufacture their own food are plants, and this is mainly because of the presence of specialized structures in the plant cell.
Australia has discovered the world's largest and oldest known living plant. Posidonia australis is an ancient and extremely hardy seagrass discovered in Shark Bay, Western Australia. It's at least 4,500 years old and stretches across 180 kilometres of shallow ocean.