Single-leaf Pinyon

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Single-leaf Pinyon

Single-leaf Pinyon (Pinus monophylla subsp. monophylla) leaves and immature cones

Kingdom:	Plantae
Division:	Pinophyta
Class:	Pinopsida
Order:	Pinales
Family:	Pinaceae
Genus:	Pinus
Subgenus:	Ducampopinus
Species:	P. monophylla

Binomial name

Pinus monophylla
Torr. & Frém.

The Single-leaf Pinyon (Pinus monophylla) is a pine in the pinyon pine group, native to the United States and northwest Mexico. The range is in southernmost Idaho, western Utah, Arizona, southwest New Mexico, Nevada, eastern and southern California and northern Baja California. It occurs at moderate altitudes from 1200-2300 m, rarely as low as 950 m and as high as 2900 m. It is widespread and often abundant in this region, forming extensive open woodlands, often mixed with junipers.

Isolated Single-leaf Pinyon in open Utah Juniper woodland, Pah Rah Range, Nevada

It is a small to medium size tree, reaching 10-20 m tall and with a trunk diameter of up to 80 cm, rarely more. The bark is irregularly furrowed and scaly. The leaves ('needles') are, uniquely for a pine, usually single (not two or more in a fascicle, though trees with needles in pairs are found occasionally), stout, 4-6 cm long, and grey-green to strongly glaucous blue-green, with stomata over the whole needle surface (and on both inner and outer surfaces of paired needles). The cones are acute-globose, the largest of the true pinyons, 4.5-8 cm long and broad when closed, green at first, ripening yellow-buff when 18-20 months old, with only a small number of very thick scales, typically 8-20 fertile scales. The cones open to 6-9 cm broad when mature, holding the seeds on the scales after opening. The seeds are 11-16 mm long, with a thin shell, a white endosperm, and a vestigial 1-2 mm wing; they are dispersed by the Pinyon Jay, which plucks the seeds out of the open cones. The jay, which uses the seeds as a food resource, stores many of the seeds for later use by burying them. Some of these stored seeds are not used and are able to grow into new trees. Indeed, Pinyon seeds will rarely germinate in the wild unless they are cached by jays or other animals.

There are three subspecies:

Pinus monophylla subsp. monophylla. Most of the range, except for the areas below. Needles more stout, bright blue-green, with few resin canals. Cones 5.5-8 cm long, often longer than broad.
Pinus monophylla subsp. californiarum (D. K. Bailey) Zavarin. Southernmost Nevada, southwest through southeastern California (northwest only as far as the San Jacinto Mountains) to 29°N in northern Baja California. Needles less stout, gray-green, with few resin canals. Cones 4.5-6 cm long, broader than long.
Pinus monophylla subsp. fallax (E. L. Little) Zavarin. Slopes of the lower Colorado River valley and adjacent tributaries from St. George, Utah to the Hualapai Mountains, and along the lower flank of the Mogollon Rim to Silver City, New Mexico. Needles less stout, gray-green, with numerous resin canals. Cones 4.5-6 cm long, broader than long.

It is most closely related to the Colorado Pinyon, which hybridises with it (both subsps. monophylla and fallax) occasionally where their ranges meet in western Arizona and Utah. It also (subsp. californiarum) hybridises extensively with Parry Pinyon.

An isolated population of trees in the New York Mountains of southeast California with needles mostly in pairs, previously thought to be Colorado Pinyons, have recently been shown to be a two-needled variant of Single-leaf Pinyon from chemical and genetic evidence. Occasional two-needled pinyons in northern Baja California are hybrids between Single-leaf Pinyon and Parry Pinyon.

[edit] Uses and symbolism

The edible seeds, pine nuts, are extensively collected throughout its range; in many areas, the seed harvest rights are owned by Native American tribes, for whom the species is of immense cultural and economic importance. During the mid nineteenth century many Pinyon groves were cut down to make charcoal for ore-processing, destroying the traditional lifestyle of the Native Americans who depended on them for food. When the railroads penetrated these areas, imported coal supplanted locally-produced charcoal.

Anchor chain formerly used for clearing woodlands in western Nevada

Following the resulting re-establishment of Pinyon woodlands, many ranchers became concerned that these woodlands provided decreased livestock forage. Efforts to clear these woodlands, often using a surplus battleship chain dragged between two bulldozers, peaked in the 1950s, but were subsequently abandoned when no improved forage resulted. The destruction of large areas of Pinyon woodlands in the interests of mining and cattle ranching is seen by many as an act of major ecological and cultural vandalism. Single-leaf Pinyon is also occasionally planted as an ornamental tree and sometimes used as a christmas tree. It is rarely seen in nurseries, because it is difficult to germinate.

The Single-leaf Pinyon is the official state tree of the state of Nevada, USA.