Pinus aristata / Rocky Mountain bristlecone pine

subgenus Strobus (Lemmon), section Parrya (Mayr), subsection Balfourianae (Engelmann).

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.

artwork courtesy of University of South Florida
artwork courtesy of University of South Florida

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.
Natural range of <em>Pinus aristata </em>
Natural range of Pinus aristata

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.

Attribution from: R. Kral; Pinus. Flora of North America Editorial Committee (eds.): Flora of North America North of Mexico, Vol. 2; ©1993 Oxford University Press.

Ancient Rocky Mountain bristlecone pines (Pinus aristata) on Windy Ridge in the Bristlecone Pine Scenic Area of Pike National Forest, Colorado.
Photo by David Rasch
Picture from one of 3 specimens grown by myself from seed. These trees have reached a height of 6 meters in 21 years of growth and made their first cones in 2001.
Photo by Ken Copeland
Bud breaking. Spring growth on specimen in my garden
Photo by Ken Copeland
Typical resin flecks of Pinus aristata, the Rocky Mountain bristlecone pine.
Photo by Hans G. Oberlack via Wikipedia
Pinus aristata foliage and cone with bristle. Pike and San Isabel National Forests, south-central Colorado.
Photo by Dave Powell, USDA
Pinus aristata foliage and cone with bristle. Pike and San Isabel National Forests, south-central Colorado.
Photo by Jeffrey J. Witcosky, USDA Forest Service
Rocky Mountain bristlecone pine (Pinus aristata) in the Prague Botanic Garden, Prague, Czech Republic.
Photo by Karelj via Wikipedia
Picea engelmannii (blue) and Pinus aristata (green, far left), Humphreys Peak, Arizona.
Photo by Andrew Petro
Pinus aristata between Mt. Hope (4247 m) and Quail Mountain (4103 m), San Isabel National Forest, Buena Vista, Colorado.
Photo by Jeremiah LaRocco via Wikipedia
Stunted Pinus aristata, Humphreys Peak, Arizona.
Photo by Andrew Petro

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