Pinus aristata, first described in 1862 by Georg Engelmann (1809–1884) is commonly known as Rocky Mountain bristlecone pine or Colorado bristlecone pine. The scientific name refers to the cones' prickliness or arista. Pinus aristata is currently regarded as one of three closely related species collectively known as bristlecone pines. In addition to its informal and regional names, the trees are referred to as the bristlecone, foxtail or hickory pine.
Description. Rocky Mountain bristlecone pine is an evergreen coniferous species of tree that grows to mature heights of 50 feet (15 m) with a strongly tapering, twisted trunk up to 3 feet (1 m) in diameter, measured at breast height. The tree's crown is rounded, flattened (sheared), or irregular.
Bark is gray to red-brown colored and shallowly fissured, with long, flat, irregular ridges.
Branches are contorted; puberulent twigs are pale red-brown colored, aging gray. Young branches resemble long bottle brushes because of persistent leaves.
Buds ovoid-acuminate shape, pale red-brown color, circa 0.4 inch (1 cm), and resinous.
Upcurved Leaves (needles) grow in bundles of 5 per fascicle, and persist 10 to 17 years on the tree. They grow to lengths of 1.2 to 1.6 inches (3 - 4 cm) and 0.032 to 0.04 inch (0.8 - 1 mm) thick, deep Blue-green colored, with drops and scales of resin. No other pine exhibits this behavior and this habit is often confused with scale insect infestations.
Pollen cones are ellipsoid shaped, circa 0.4 inch (10 mm) long and bluish to red colored.
Seed cones mature in 2 years, shedding seeds and falling soon thereafter. They are spreading, symmetric, lance-cylindric shaped before opening, lance-ovoid to ovoid or cylindric when open, 2.4 to 3.3 inches (6 - 11 cm) long, purple to brown colored, with triangular base, extended into slender, brittle prickle (arista) 0.16 to 0.4 inch (4 - 10 mm) long.
Seeds are obliquely obovoid shaped with a 0.2 to 0.24 inch (5 - 6 mm) body. They are gray-brown to near black colored with a 0.4 to 0.52 inch (10-13 mm) wing.
Distribution. This species is native to montane to subalpine areas of USA — Colorado, New Mexico and Arizona (the San Francisco Peaks), growing at elevations of 7,500 to 12,000 feet (2,300 - 3,650 m) above sea level.
It is hardy to USDA Zone 3 — cold hardiness limit between -40° and -30°F (-39.9° and -34.4°C).
Pinus aristata is a very attractive slow-growing, small to medium-sized tree suitable for small gardens in cold climates. Even so, it is never as long-lived as it is in the wild of the high desert. Typically the bristlecone lives less than 100 years before it succumbs to root decay in the warmer, moister conditions prevalent in most inhabited places.
The oldest Pinus aristata, which grows high on Black Mountain in Colorado, was found to have at 2,435-year tree ring record (and overall estimated age of 2,480 years, per Craig Brunstein) in 1992. However, trees there rarely live over 1,500 years.
Once thought to be the world's oldest living tree, that honor is now going to the related species, Pinus longaeva, (D.K. Bailey) discovered in the White Mountains of California. In the 1970s, scientists differentiated the Pinus longeava, the Great Basin bristlecone pine, from the shorter-lived Pinus aristata, the Rocky Mountain bristlecone pine, which grows in the southwestern mountains of Colorado and New Mexico.