Bristlecone Pine, common name for a cone-bearing evergreen tree native to high, dry mountainous areas in the western United States. Bristlecone pines, named for the bristlelike prickles on the cone scales, are renowned for their longevity; some specimens have reached ages of 3000 to 5000 years, making bristlecone pines prometheus the oldest known living trees. Only two scattered populations of the trees exist—the Rocky Mountain bristlecone grows in Colorado and Utah, and the Great Basin bristlecone is found primarily in the White and Panamint mountains of southeastern California.

Bristlecone pines grow extremely slowly. In 100 years they may produce less than 2.5 cm (1 in) of growth rings on the trunk. One 700-year-old tree was found to be only 90 cm (3 ft) tall, with a trunk diameter of 7.5 cm (3 in). The oldest trees, found in the White Mountains, are weathered and misshapen. Typically, they have only one live branch with a few twigs bearing needles; they cling to life by a narrow ribbon of living bark that transports water upward from the soil. Unlike most trees, in which dead wood rots, weakening the trees and leading to their fall, the dead wood of the bristlecone pines remains solid.

The bristlecone pine can attain heights of 20 m (65 ft), but this is rare and occurs only at lower elevations. The bark is green and smooth on young trees and becomes scaly with age. The short, stiff, dark bluish-green needles are arranged in groups of five and are usually covered with specks of whitish resin, or sap. The needles are retained for 12 to 20 years (most pines retain their needles for 2 or 3 years). Small, reddish or purple cones appear in July and August. They develop into hard, reddish-brown cones, up to 9 cm (3.5 in) long, and ripen in September and October. The seeds are 7 to 10 mm (0.3 to 0.4 in) long.

Because of the renowned longevity of the bristlecone pine, the history of past climates is recorded in the details of the trees’ growth rings. This information gave rise to the science of dendrochronology, the use of tree growth rings for dating historic events and changes in the environment.

Scientific classification: The bristlecone pine belongs to the pine family, Pinaceae. It is classified as Pinus aristata, although some sources now consider the Great Basin population to be a separate species, classified as Pinus longaeva.