Pinus reflexa (southwestern white pine) description

Conservation Status

Pinus reflexa

(Engelm.) Engelm. (1882)

Common names

Southwestern white pine. This is also the common English name of Pinus strobiformis. Now that P. reflexa is recognized as a distinct species, all trees formerly called P. strobiformis in the U.S. (as well as some in Mexico) are now reassigned to P. reflexa. These American trees have been called "southwestern white pine" since the late 1800s.

Taxonomic notes

Type: USA, Arizona, Santa Rita Mountains, J. T. Rothrock 654 (lectotype MO). Syn. Pinus ayacahuite var. reflexa (Engelm.) Voss, P. flexilis var. reflexa Engelm. (1878), P. flexilis subsp. reflexa (Engelm.) A.E.Murray.

George Engelmann described this taxon in 1878 as a variety of Pinus flexilis. After consideration, in 1882 he raised it to species rank, citing morphological differences in the seed cone. Almost no one accepted this idea, though, and it remained a variety in most publications persisting into the 21st century (e.g., Farjon 2010). However, authors as early as Engelmann recognized that P. flexilis and P. strobiformis form a cline, showing continuous variation in ecological, morphological and molecular characters, a subject addressed in detail in the "Taxonomic notes" section of P. strobiformis. Briefly, populations intermediate between these two species occur from southern Colorado to the northern Sierra Madre (Menon et al. 2017). Trees in this transitional area are now referred to Pinus reflexa. The cline, by the way, becomes more complex in Mexico, where it includes P. veitchii, P. ayacahuite, P. strobiformis, and P. stylesii.

It is debatable whether P. reflexa should be treated at species rank. It is certainly convenient to treat it as a species, since it is readily distinguishable from both P. flexilis and P. strobiformis using ecological, morphological, distributional, or molecular evidence (Bisbee 2014, Menon et al. 2017). I here treat it at species rank primarily because of this convenience, and because POWO and other databases that rely upon POWO are treating it as such. But in a sense it is not a "real" species; it does not seem to have been recorded in the paleobotanical record and it readily interbreeds with both species mentioned above. It should properly be regarded as a nothospecies, Pinus × reflexa.

Description

Engelmann (1878) says simply "Leaves in fives, mostly entire and smooth-edged, 1.4-2’ long, in a loose, deciduous sheath, about 4’ in length... cones ovate-cylindrical, about 4’ long; apophysis elongated, reflexed." Little (1980) provides a more comprehensive description based primarily on work with American trees; he says it is a tree 15-24 m tall and 50-90 cm dbh with a straight trunk and narrow, conical crown of horizontal branches. Bark first gray and smooth, with age turning dark gray or brown and becoming furrowed into irregular longitudinal ridges. Leaves in fascicles of 5, evergreen, sheath deciduous, 6-9 cm long, slender, pliable, serrulate at least near the apex, bright green with stomata only on inner surfaces. Seed cones 15-23 cm long, cylindrical, yellow-brown, short-stalked, opening at maturity; cone scales slightly thickened, very long, with a thin narrow spreading recurved apex. Seeds large, very short-winged (this description also reflects my observations of the tree). See García Esteban et al. (2004) (as P. flexilis var. reflexa) for a detailed characterization of the wood anatomy.

Frankis (2008) observes that P. reflexa differs from P. strobiformis in having "partly serrulate needles, very rarely entire or fully serrulate, with the serration mainly in the apical half of the leaf and entire in the basal half; shorter mean cone length, unstriated smooth glossy buff-yellow scales with less prolonged apophyses, basal scales not or less revolute, and smaller (primarily narrower) seeds." Note that despite the epithet reflexa, a fully reflexed apophysis is not necessary, but can be observed in some specimens of both species.

Distribution and Ecology

USA: SW Colorado, Arizona, New Mexico and W Texas; Mexico: Sonora, Chihuahua, Coahuila, Nuevo León (Frankis 2008, Bisbee 2014). Occurrences are at montane elevations of 1520-3000 m (based on 145 records on GBIF). Typically found in mixed conifer forest with pines such as Pinus arizonica, P. brachyptera, and P. engelmannii; often also Abies concolor and Quercus spp. (pers. obs. in Arizona, Colorado and New Mexico, 2012-2022).

Distribution: Yellow is P. reflexa, red is P. strobiformis, blue is P. veitchii. Data source for P. reflexa is GBIF (2026).

White pine blister rust (Cronartium ribicola), an introduced fungal disease, has afflicted this and certain other white pines. Pinus reflexa is also a principal host for the dwarf mistletoes Arceuthobium apachecum and A. blumeri (Hawksworth and Wiens 1996).

In 2011 the IUCN assessed Pinus strobiformis as of "Least Concern" for conservation due to its extensive distribution and relatively stable population. Although that assessment is dated, does not address climate change, and conflates P. strobiformis with P. reflexa, still the "Least Concern" determination probably applies under current criteria.

Remarkable Specimens

In the United States, the largest is 150 cm dbh with a height of 34 m and a crown spread of 19 m, located in Lincoln National Forest, NM (American Forests 1996; identified as P. strobiformis). The tallest is a tree 38.9 m tall in the Jones Creek watershed, San Juan Mountains, Colorado, discovered and measured in 2014 (Robert Van Pelt email 2014.08.17). As of 2026 it is not known whether either of these trees is still alive.

The oldest recorded specimen was Tree VPK02, collected in the San Mateo Mountains of New Mexico by Henri Grissino-Mayer, J. Speer, and K. Morino; it had a crossdated age of 599 years (RMTRR 2006). It is not known if this tree was alive at the time. The oldest known living specimen, 439 years, was documented in a tree-ring chronology covering the period 1249-1991, collected in the Pinaleño Mountains of southern Arizona by Henri Grissino-Mayer and Chris Baisan (doi.org/10.25921/s72r-cp71).

Ethnobotany

The seeds were eaten by natives of the southwest U.S. (Little 1980). Although winged, the seeds are relatively large for a pine.

Observations

It can easily be found in montane mixed forests of the "sky island" ranges of southern Arizona, including the Pinal, Pinaleño, Catalina, Rincon, Santa Rita, Huachuca, and Chiricahua ranges.

Remarks

The epithet reflexa refers to the reflexed cone apophysis (Engelmann 1878).

Citations

American Forests 1996. The 1996-1997 National Register of Big Trees. Washington, DC: American Forests.

Bisbee, Jeff. 2014. Cone morphology of the Pinus flexilis-strobiformis complex of the western United States and Mexico. Bulletin of the Cupressus Conservation Project 3:3-33. Available: https://www.cupressus.net/bulletin/bulletin05/BullCCP03_1.pdf, accessed 2026.05.11.

Engelmann, George. 1878. P. 258 in J. T. Rothrock, Report upon United States Geographical Surveys West of the One Hundredth Meridian, in Charge of First Lieut. Wheeler ... vol. 6 - Botany. Available: Biodiversity Heritage Library, accessed 2026.05.11.

Engelmann, George. 1882. Notes on Western Conifers. Botanical Gazette 7(1):4. Available: Biodiversity Heritage Library, accessed 2026.05.11.

Frankis, Michael. 2008. The high altitude white pines of Mexico and the adjacent SW USA (Pinus L. subgenus Strobus Lemmon, Pinaceae). International Dendrology Society Yearbook 2008: 64-72.

GBIF. 2026.05.11. GBIF Occurrence Download https://doi.org/10.15468/dl.y5uvyy.

Hawksworth, F. G. and D. Wiens. 1996. Dwarf mistletoes: Biology, pathology and systematics. Agriculture Handbook 709. Washington, DC: U.S.D.A. Forest Service.

Menon, M., J. C. Bagley, C. J. Friedline, et al. 2018. The role of hybridization during ecological divergence of southwestern white pine (Pinus strobiformis) and limber pine (P. flexilis). Molecular Ecology 27:1245–1260.