Hartweg's Pine

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Hartweg's Pine

Hartweg's Pines in Marquesa National Forest, between Mexico City and Toluca, Mexico, at about 3,500 m altitude

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

Binomial name

Pinus hartwegii
Lindl.

Hartweg's Pine (Pinus hartwegii; syn. P. rudis, P. donnell-smithii) is a pine native to the mountains of Mexico and Central America east to Honduras. It is a very high altitude species, growing at altitudes of 2500-4300 m, and forms the alpine tree line on most of Mexico's higher mountains. It is named after Karl Theodor Hartweg, who discovered it in 1838. It grows on both mountain ranges Sierra Madre Occidental and Sierra Madre Oriental (29° North latitude) from Chihuahua State and Nuevo León (26°) to the highest peaks on the Mountains of El Salvador- Honduras border (15° North latitude). On Sierra Madre Occidental there is a type of this pine that grows with very dry winters and a very heavy rainy season in summer, with constant frosts from October to March. This pine does not acquire the dwarfed and contorted shape that many trees do at high altitudes, even it reaches the alpine tree line, this tree is not damaged by harmful consequences of cold and wind-blown ice of altitude, Pinus hartwegii has been recently very studied due to that property as an evolutionary unique member on tree line ecophysiology.

It is an evergreen tree reaching 20-30 m in height, with a broad, rounded crown. The bark is thick, dark grey-brown, and scaly or fissured. The leaves are needle-like, dark green, five (occasionally four) per fascicle, 10-20 cm long and 1.2-1.5 mm wide, the persistent fascicle sheath 1.5-2 cm long. The cones are ovoid, 6-13 cm long, black or very dark purple, opening when mature in spring to 5-7 cm broad. The seeds are winged, 5-6 mm long with a 1.5-2.5 cm wing. Pollination is in late spring, with the cones maturing 20-22 months after.

It is closely related to Montezuma Pine (P. montezumae), differing from it in the shorter leaves, black (not brown) and smaller cones; it replaces Montezuma Pine at high altitudes, and often hybridises with it where they meet at middle altitudes.