Pinus × rhaetica / Rhætic pine

Pinus × rhaetica, as described in 1864 by Christian Georg Brügger (1833–1899) in Flora 47, is commonly known as Rhætic pine, The species name refers to the Rhætica 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.

  • Bark is often darker red on the branches than in Scots pine, but usually still smooth and scaly, while the trunk is grayer and more frequently divided into irregular plates.
  • Leaves (needles) are quite variable, colored from dark green, like P. mugo to the typical bluish green of P. sylvestris, depending where along the intergrade zone they exist.
  • Seed cones follow the same pattern. If the tree more resembles Mountain pine, the first-year cones will slightly recurve, while if the tree more resemble Scots pine, the first-year cones are held upright.
Given these points, it is hard to distinguish the hybrids from extreme variants within the parent species. Regardless, hybrids are considered to be rare in nature given their only slightly overlapping habitats and narrow windows of when both species are actively releasing pollen.

Hardy to USDA Zone 3 — cold hardiness limit between -40° and -30°F (-39.9° and -34.4°C).

Attribution from: James E. Eckenwalder; Conifers of the World: The Complete Reference; ©2009, Timber Press, Portland, OR.

Pinus × rhaetica — bark detail.
Photo by Zoya Akulova
Pinus × rhaetica — seed cone detail.

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