The oldest known dated living trees are Intermountain Bristlecone Pines more than 4,600 years old, protected at Inyo National Forest near Bishop, in eastern California. Other very old Intermountain Bristlecone Pines are found at Wheeler Peak Scenic Area, in the Humboldt National Forest of eastern Nevada. Although these trees are classed among the oldest known living things, some shrubs and trees that spread in colonies or clumps from the same root system may be older. The age of a tree is dated by counting the annual rings of wood produced by the cambium layer inside the bark. Wood cells formed in the spring are generally large, while those formed in the summer are smaller; the contrast in cell size from one year to the next is visible as a line. In an old Bristlecone Pine, small cores of wood are removed at different places around the trunk to locate the oldest ring in the center. Intermountain Bristlecone Pine used to be considered a variety of P. aristata.
Find native plant species by state. Each list contains commercially available species suitable for gardens and planned landscapes. Once you have selected a collection, you can browse the collection or search within it using the combination search.View Recommended Species page