This is a list of the oldest-known trees. Definitions of longevity vary between clonal trees, ones where parts of the tree continue to live after the death of the first trunk or trunks, and non-clonal trees. Tree ages are derived from a variety of sources, including documented "tree-ring" (dendrochronological) count core samples, radiocarbon dating, girth-to-age formulas, and estimates from growth rates. For these reasons, there are three lists of "oldest trees" here, using different criteria.
The three tables of trees are listed by age and species. The first table includes trees for which a minimum age has been directly determined, either through counting or cross-referencing tree rings or through radiocarbon dating. Many of these trees may be even older than their listed ages, but the oldest wood in the tree has rotted away. For some old trees, so much of the center is missing that their age cannot be directly determined. Instead, estimates are made based on the tree's size and presumed growth rate. The second table includes trees with these estimated ages. The last table lists clonal colonies in which no individual tree trunks may be remarkably old but in which the organism as a whole is thought to be very old.