Arboretum: Pinus flexilis, Limber pine
The common name of this pine tree refers to its tough, flexible twigs. Limber pines are native to the Rocky Mountains from Canada through New Mexico where they grow on a range of elevations, most typically higher windswept slopes. It’s a long-lived tree; many in the western mountains are thought to be up to 1000 years old.
This is not a tall pine like Pinus strobus, the white pine. In its native range, Pinus flexilis can reach up to 70 feet but even less on more exposed sites. In our East Coast landscapes Pinus flexilis stays closer to 30 or 40 feet, therefore making it a good tree for confined areas.
The stiff needles are 2 ½ to 3 ½ inches long and clustered in groups of five, predominantly at the branch tips. The cones are 3 to 6 inches long. Out West, the seeds are a favorite of the Clark’s nutcracker, a bird that literally harvests them from the cones, collecting them in a specialized pouch, and then hides the cache which ensures food for the bird and wide seed dispersal for the tree.
Haverford College’s tree collection includes several young specimens in the Pinetum along Haverford Road that were planted to replace mature limber pines lost over the years. Our state champion, the largest measured Pinus flexilis in Pennsylvania, was among those that recently died.
A cultivar, Pinus flexilis ‘Vanderwolf’s Pyramid’, is planted at our new dorm site. It’s the best of the blue foliage forms with bright blue-green needles and has a denser, more uniform pyramidal shape than the straight species, so it’s a popular cultivar for home gardens.