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 shared by many species at high altitudes. Even at the alpine tree line, this tree is not damaged by the cold and wind-blown ice present at that altitude. Consequently, Pinus hartwegii has been studied as an evolutionary unique member on tree line ecophysiology.