Pinus×hunnewellii, as described in 1952 by Albert G. Johnson, in Journal of the Arnold Arboretum, vol.33, is commonly known as Hunnewell's white pine, named for Hunnewell Arboretum in Wellesley, Massachusetts where it was originally found in 1949.
Description. Hunnewell's white pine is a spontaneous garden hybrid that has been recreated deliberately. The parent species' are two naturally geographically, widely separated, typical white pines in subsection Strobus, namely Japanese white pine (Pinus parviflora) and Eastern white pine (Pinus strobus). It is similar to both parents in their shared characteristics and intermediate or generally favoring one or the other in the features in which they differ. The original trees found has P. strobus as the seed parent. The reciprocal hybrid has proven to be rather difficult to recreate, probably due to the difference is seed sizes.
It is faster growing than both parents, displaying strong "hybrid vigor," and has a loose, open crown whose irregularity is accentuated by susceptibility to white pine weevil, which kills the lead shoots. This hybrid vigor also presents itself in forking of terminal shoots and even seed cones. Further, lateral branches often turn upward resulting in the creation of new lead shoots.
Bark is scaly like that of Japanese white pine rather than ridged like that of Eastern white pine.
Twigs are minutely hairy, more so than either parent.
Leaves (needles) are in fascicles of 5, measuring 2.6 to 3.4 inches (6.5 - 8.5 cm) long, which is in the mid-range for P. strobus and longer-than-normal for P. parviflora. However, like the Japanese white pine, the needles are twisted, curved and more Blue-green than needles seen in P. strobus.
Pollen cones are pink in color, like those on Japanese white pine, but are grouped in an elongate cluster, unlike the tight cluster of yellow pollen cones typical of Eastern white pine.
Seed cones are on short peduncles with a flat base as is seen in P. parviflora, but are the same length as P. strobus cones. The hybrid cones are composed of more seed scales than either parent.
Seeds are of intermediate length of the parents. At 0.28 to 0.36 inch (7 - 9 mm) long, they are smaller than those of Japanese white pine and larger than those of Eastern white pine.
Hardy to Zone 5 — cold hardiness limit between -20° and -10°F (-28.8°C and -23.3°C).