Pinus strobiformis, as described in 1848 by Georg Engelmann (1809–1884), in Memoir of a Tour to Northern Mexico: connected with Col. Doniphan's Expedition in 1846 and 1847, is commonly known as Mexican white pine, Arizona white pine, Chihuahuan white pine, and southwestern white pine; as well as pino blanco, pinabete, and pino enano in the Spanish language. The species name describes this tree's general resemblance all members of subsection Strobus.
Ethnobotany. The seeds were eaten by the indigenous people of the southwestern U.S. It is locally (in Mexico) used for cabinetry, doors and window frames.
Description. Southwestern white pine is an evergreen coniferous species of tree that grows to mature heights of 50 to 80 feet (15 - 24 m) with a slender, straight trunk up to 20 to 36 inches (50 - 90 cm) in diameter, measuring at breast height; and a crown conic, becoming rounded to irregular with age.
Bark is smooth and silvery gray on young trees, aging to a dark grayish brown, furrowed and divided into rough rectangular plates.
Branches grow spreading-ascending;
Twigs are slender, colored pale red-brown, with a puberulous or glabrous texture, sometimes glaucous, aging gray or gray-brown, and smooth.
Foliar buds are ellipsoid shaped, resinous, red-brown in color, measuring circa 0.4 inch (1 cm).
Leaves (needles) are borne 5 per fascicle, growing spreading to ascending-upcurved, persisting 3 to 5 years on the tree. Individual needles measure 1.6 to 4 inches (4 - 10 cm) long by 0.024 to 0.04 inch (0.6 - 1 mm) thick. They are straight to slightly twisted and pliant, colored dark green to Blue-green, without evident stomatal lines on abaxial surfaces; adaxial surfaces are conspicuously whitened by narrow lines of stomata. Needle margins are sharp, razorlike and entire to finely serrulate, with narrowly acute to short-subulated apices.
Foliar sheaths measure 0.6 to 0.8 inch (1.5 - 2 cm), and shed early.
Pollen cones are cylindrically shaped, pale yellow-brown in color, and circa 0.24 to 0.4 inch (6 - 10 mm) long.
Seed cones mature 2 years after pollination, shedding seeds and falling soon thereafter, Individual cones are pendent, symmetrically lance-cylindric before opening, broadly lance-cylindric when open, creamy brown to light yellow-brown in color. measuring 6 to 10 inches (15 - 25 cm) long, with 2.4 inch (6 cm) long peduncles.
Cone scales number around 100 per cone, bearing apophyses that are somewhat thickened, and strongly cross-keeled, with a reflexed tip. Umbos are terminal and low.
Seeds are ovoid shaped, with a 0.4 to 0.52 inch (10 - 13 mm) long body, colored red-brown, and essentially wingless.
Distribution. This species is native to USA — Arizona, New Mexico, and Texas; in Mexico — Chihuahua, Coahuila, Durango, Nuevo León, Sinaloa, Sonora (type subspecies); subsp. veitchii is found in Mexico — Guanajuato, Hidalgo, México, Michoacán, Morelos, Puebla, Querétaro, Tlaxcala, and Veracruz. Populations in the U.S. and northernmost Mexico are of the reflexa type, showing characters intermediate between typical P. strobiformis and P. flexilis. Grows at elevations of 6,500 to 10,000 feet (1,900 - 3,000 m) above sea level. Habitat dry rocky slopes in high mountains, or as a minor component in mixed conifer forests. Within habitat, it mostly grows on moist, cool sites with associates such as P. hartwegii, and P. culminicola.
Hardy to USDA Zone 8 — cold hardiness limit between 10 to 20ºF (-12.1°C to -6.7°C).
Pinus strobiformis — a mature tree in habitat, south of El Salto, Durango, Mexico.
Photo by C.J. Earle
A stand of Pinus strobiformis in habitat.
Photo by Chris Schnepf, University of Idaho
Pinus strobiformis — bark detail.
Photo by C.J. Earle
Pinus strobiformis — foliage and seed cones in situ.
Photo by C.J. Earle
I'm not quite sure about the zone 8 on this one. I recently bought some seedlings that had been raised in a tree nursery in Vermont. That's hardly in zone 8. Also, based on my own memory and another website as well, this tree can be found at elevations between 8,000 and 10,000 feet in Arizona. As a former Arizona resident, I once saw a reported temperature of -40°F at Hawley Lake in the White Mountains. Zone 8? Well, I'm just not sure how those hardiness zones are arrived at.
Fred M. Cain,
That nursery in Vermont? What's the provenance of their seed? Is it possible they're working with a <em>strobiformis/strobus</em> hybrid? So many questions.
This is a great reason why we have the comments section on these records - to report on individual results. Remember, it's always safest to think in generalities. Individual results vary greatly depending on seed provenance.
In the case of<em> Pinus strobiformis</em>, we really can't grow it in the Pacific NW (USDA Zone 8). Too cold and wet in spring. So ... I usually don't pay much attention at all to published zonal hardiness. I look around and see what grows well in the area. I lack the time, patience, and money to push zones.
Dear Conifer Editor,
This website states it's hardy to zone 4<strong>:</strong>
<a href="https://landscapeplants.oregonstate.edu/plants/pinus-strobiformis" rel="nofollow">https://landscapeplants.oregonstate.edu/plants/pinus-strobiformis</a>
(I hope it's O.K. to quote that here).
This species of pine is native to relatively harsh, cold but relatively dry mountain conditions so I could well believe that it might be just a bit too wet in the Pacific Northwest. What I'm wondering is whether we might've gotten this pine confused with another Mexican White Pine that is almost certainly hardy only to zone 8. It's all kind of a mystery and confusing to me. At any rate, I will try to keep everyone posted on how mine are doing. So far they look good and the weather has been cooperating with me.