Determining the "oldest" species of plant is tricky, as the fossil record is incomplete and evolutionary lineages can be difficult to trace.

However, a strong contender for the title of oldest living plant species is "Ginkgo biloba", commonly known as the ginkgo. This species is often referred to as a "living fossil" because it has remained largely unchanged for over 200 million years, surviving even the mass extinction event that wiped out the dinosaurs.

While there might be other ancient plant species with deeper evolutionary roots, the ginkgo's longevity and resilience make it a remarkable example of an incredibly old and successful plant lineage.