Pinus × rhaetica, as described in 1864 by Christian Georg Brüsgger (1833-1899) in Flora 47, is commonly known as Rhaetic pine, The species name refers to the Rhaetica alps, located in eastern Switzerland and western Austria.
Description. Rhaetic pine described a natural hybrid of Mountain pine (Pinus mugo) and Scots pine (Pinus sylvestris), occurring occasionally throughout the the regions where the two species overlap, from the northern side of the French Pyrenees though the Alps to the Carpathians in Slovakia, usually at the junction of the sub-alpine habitat of P. mugo and the montane forests of P. sylvestris.
The hybrids are extremely variable, but generally fall intermediate between the two parents or present combinations of characteristics not found in either parent. They usually grow as trees, although some are shrubby in form.
Hardy to USDA Zone 3 - cold hardiness limit between -40° and -30°F (-39.9° and -34.4°C).