Pinus×murraybanksiana, as described in 1949 by William Palmer Stockwell (1898–1950) and Francis Irving Righter (1897 – ?), in Madroño 10(69), is commonly known as Murraybanks pine. The species name is an amalgam of the two parent species; it described natural and synthetic hybrids of Jack pine (Pinus banksiana) and lodgepole pine (Pinus contorta). The natural hybrids from the Canadian Rocky Mountains involve lodgepole pine (Pinus contorta var. latifolia), while the synthetic hybrids created in California where done so using the local Sierra Nevada tree, Pinus contorta var. murrayana. The California synthetic hybrid is the tree which provided the type that was selected at Eddy Arboretum, Placerville, California in the 1940s and named by Stockwell and Righter.
Description. Murraybanks pine is an evergreen coniferous tree that grows to mature heights of 80 feet (25 m) or more with varying resemblance to both parent species. Since the parents are superficially similar, the hybrids have few characteristic features with the exception of expected hybrid vigor; Murraybanks pine tends to grow faster than both parent species.
Bark is gray in color, similar to Jack pine.
Branches more closely resemble Lodgepole pine; they are stiff and upwardly angled, in contrast with the flexible, lax branching seen in Jack pine.
Leaves (needles), at 1.2 to 2 inches (3 - 5 cm) long are intermediate of the parents, longer than the typical P. banksiana and a bit shorter than the needles of P. contorta.
Seed cones are extremely variable, probably due to variations in which variety of Pinus contorta was used in the parentage. In either case, seed cones are long persistent on the tree. In natural hybrids (P. contorta var. latifolia parentage), the cones are asymmetrical, usually curled and remain closed at maturity; while the synthetic hybrids (P. contorta var. murrayana parentage), have symmetrically straight cones that open widely at maturity to shed seeds, but are nonetheless persistent on the tree. Regardless of parentage, hybrid seed cones lack the prominent doming of the exposed portions of the lower seed scales on the side away from the twig that is typical in Lodgepole pine, and they have much shorter prickles, no longer than 0.04 inch (1 mm).
Seeds resemble both parent species and are generally viable allowing advanced generation hybids as well as back-crosses.
Distribution. The natural hybrids are restricted to the region of overlap of the parent species in the foothills of the Rocky Mountains in western Canada, mostly Alberta. Although they also exist in Northwest Territories, they have not been extensively studied.
Hardy to USDA Zone 3 — cold hardiness limit between -40° and -30°F (-39.9° and -34.4°C).
Comments