Pinus monophylla (singleleaf piñon) description

Pinus monophylla

Torr. & Frém. 1845

Common names

Singleleaf piñon (or pinyon) (Arno and Gyer 1973); one-leaved, Gray, Frémont, or Nevada nut pine (Peattie 1950). Note that since there are 3 taxa of singleleaf piñons, a more explicit name is desirable; I call it "Great Basin piñon" because its range is almost wholly within the Great Basin, and there are no other piñons in that area.

Taxonomic notes

See Pinus cembroides for a general introduction to the phylogenetics of the piñons, a subject that has been greatly clarified by some highly detailed molecular studies (Montes et al. 2019, Buck et al. 2020, Buck et al. 2023). One outcome of those studies is that the species P. californiarum, P. edulis, P. monophylla and P. quadrifolia form a monophyletic clade within subsection Cembroides, which is consistent with the views of most prior authors. More surprising is the news that P. californiarum and P. monophylla are not only distinct species, but they are not even sister species; P. monophylla is sister to P. quadrifolia. This finding disagreed with nearly every contemporary authority, all of whom saw only a single species of 1-needled piñon. Based on this work, we can now identify three taxa of 1-needled piñon:

The predominant piñon of the Great Basin, Pinus monophylla;
The southern California desert piñon, Pinus californiarum; and
The hybrid of Pinus californiarum and P. edulis, P. × kohae.

See P. californiarum and P. edulis for a detailed discussion of those taxa. Nonetheless, these distinct taxa also hybridize through part of their range. Buck et al. (2023) mapped much of this variability, finding substantial areas of introgression between P. californiarum and P. quadrifolia; P. californiarum and P. monophylla; and P. californiarum and P. edulis. There are also areas with 3-species introgression. They describe this as a syngameon, i.e. a "multispecies interbreeding network", wherein "species remain morphologically and genetically distinct at range cores and are able to maintain species boundaries while undergoing extensive gene flow in areas of sympatry at range peripheries. Additionally, the syngameon seems to be structured with several ‘hub species’ that contribute more genetic information than they receive and are connected to every other species through gene flow". There are important ecological consequences because each of these taxa occupies a distinct climate.

As for Pinus monophylla sensu strictu, the type is USA: California: J.C. Frémont 367 (holo NY). Synonymy:

Pinus fremontiana Endl. 1847, nom. superfl.;
Pinus edulis Engelm. var. monophylla (Torr. & Frém.) Torr. ex J.C.Ives 1860;
Caryopitys monophylla (Torr. & Frém.) Rydb. 1905;
Pinus cembroides Zucc. var. monophylla (Torr. & Frém.) Voss 1908;
Pinus cembroides Zucc. subsp. monophylla (Torr. & Frém.) A.E.Murray 1982.

With regard to the first two synonyms above, Little (1968) explains "Variation in number of needles in a fascicle has long been observed among the pinyons. For example, the type specimen and plate of Pinus monophylla Torr. & Frém. both have rare 2-needle fascicles. P. fremontiana Endlicher was a renaming of P. monophyllus, apparently because the needles were thought to be paired and cohering rather than single. P. edulis var. monophyllus Torr. apparently was intended to unite both species, though under the later binomial. Among those giving additional reasons for combining the two were J. S. Newberry and Thomas Meehan".

Description

Trees to 14 m tall and 100 cm dbh, strongly tapering, often with multiple stems, and a rounded, dense crown of spreading and ascending branches. Bark red-brown, irregularly furrowed or cross-checked, scaly. Twigs stout, orange-brown, aging brown to gray, sometimes sparsely puberulent. Buds ellipsoid, light red-brown, 5-7 mm, resinous; scale margins fringed. Needles 1 (rarely 2) per fascicle, ascending, persisting 4-6(-10) years, 20-60 x 1.3-1.6 mm, stout, curved, round (though often 2-grooved), gray-green, surfaced with 15-35 stomatal lines, margins entire, apex subulate, having 2-7 resin canals; sheath 5-10 mm, scales soon recurved, forming rosette, shed early. Pollen cones ellipsoid, ca. 10 mm, yellow. Seed cones maturing in 2 years, shedding seeds and falling soon thereafter, spreading, symmetric, ovoid before opening, broadly depressed-ovoid to nearly globose when open, 6-7 cm diameter, pale yellow-brown, nearly sessile; apophyses thickened, slightly raised; umbo subcentral, raised or depressed, nearly truncate, apiculate. As with other piñons, the seeds rest in a deep cone-scale declivity and upper cone scale tissue holds the seeds in place, so seeds do not readily fall out and are readily available to avian dispersers. Seeds cylindric-ellipsoid; body 16-18 mm, gray-brown to brown, wingless, edible, within a shell 0.25-0.35 mm thick. 2n=24 (Little 1980, Kral 1993, R. Lanner email 1999.12.20).

Cole et al. (2008) provides a key to distinguish the three taxa of 1-needled pinyons. Performing all measurements requires close examination. Near the mid-point of several representative needles, measure the following:

Count the number of stomatal lines on the needle. Best to use a dissecting microscope or high-resolution macro photos.
Measure the average diameter of the needle on two perpendicular axes. Requires a micrometer.
Count the number of resin canals in a needle cross-section. Requires some practice to get a good thin section with a razor blade; inspect under microscope at 100X.

The species can then be distingished as follows (quoted from Cole et al. 2008):

P. × kohae – fascicles contain one needle, needles are thin, 0.8–1.2 mm in diameter when dried, contain 2-3 resin ducts and 8–16 stomatal lines.

P. monophylla – fascicles contain one needle, needles are stout, 1.3–1.7 mm in diameter when dried, contain 2-7 resin ducts and 17–30 stomatal lines.

P. californiarum – fascicles contain one needle, needles are stout, 1.2–1.6 mm in diameter when dried, contain 8–16 resin ducts and 13–18 stomatal lines.

Also, the three taxa have largely disjunct distributions (map presented below). In areas where the distributions overlap, genetic analysis (Buck et al. 2023) indicates extensive introgression and the trees are best described as members of the singleleaf piñon syngameon. The genetic analysis by Buck et al. (2023) also used a mixing model to assess the portion of the genome at each sample site that was contributed by each parent species. In summary, they found:

If a tree looks like P. monophylla, it has near 100% P. monophylla genes.
If a tree looks like P. quadrifolia, it has near 100% P. quadrifolia genes.
If a tree looks like P. edulis and you're distant from P. × kohae or P. monophylla, then it has 100% P. edulis genes. In border areas, it has at least 80% P. edulis genes with admixed P. californiarum and/or P. monophylla genes.
If a tree looks like P. californiarum, it has at least 90% P. californiarum genes.
If a tree looks like P. x kohae, it has at least 20% P. californiarum and 20% P. edulis genes, and in northerly areas (N of about 36°) it can also be up to 30% P. monophylla genes.
At any site where 2 or more of the 4 taxa (P. californiarum, edulis, monophylla, quadrifolia) co-occur, a significant fraction of the trees are likely to be hybrids, and some will not be identifiable with confidence.
P. monophylla x P. californiarum hybrids are particularly common in the Joshua Tree National Park area and in Nevada S of the Spring Mountains.

Distribution and Ecology

USA: Idaho, Utah, Nevada, Arizona, California; at elevations of 1000-2300 m. Generally occurs on dry, gravelly slopes in semiarid country (Little 1980, Kral 1993). Hardy to Zone 6 (cold hardiness limit between -23.2°C and -17.8°C) (Bannister and Neuner 2001). The IUCN classifies this species as "Least Concern" for human impacts due to the extremely large extent of occurrence.

Distribution map. Green represents P. monophylla, red is P. californiarum, purple is P. edulis, blue is P. × kohae, and orange is P. quadrifolia. Pinus californiarum, P. × kohae, and P. monophylla polygons by Cole (2003), based on a climate-calibrated habitat model. P. edulis and P. quadrifolia polygons by USGS (1999), based on professional judgement by E. L. Little. All point data from GBIF, DOIs = https://doi.org/10.15468/dl.twthv7 (P. californiarum), https://doi.org/10.15468/dl.7acmds (P. × kohae), https://doi.org/10.15468/dl.5unbjc (P. monophylla), and https://doi.org/10.15468/dl.qugjbg (P. quadrifolia); all accessed 2023.03.11. GBIF data processed to add coordinates based on narrative descriptions, and remove duplicates.

Within its range, P. monophylla is generally the predominant tree species, dominating large areas throughout isolated mountain ranges of the Great Basin. In most of that area it forms piñon-juniper woodlands with species of Juniperus, primarily J. osteosperma; the pine tends to predominate at higher/wetter elevations, and the juniper at lower/drier ones. At high elevations it commonly occurs with bristlecone pine, Pinus longaeva. In other areas it may be found growing with P. ponderosa, P. jeffreyi, Abies concolor, Juniperus grandis, J. occidentalis, and various species of Ephedra. In some areas its distribution adjoins that of other piñons. This occurs with P. edulis in Utah along the front separating the Great Basin from the Colorado Plateau, and with P. × kohae across the western portion of that taxon's distribution. All three of these 1-needled piñons occur together in southern Clark County, Nevada and through much of eastern San Bernardino County, California. Co-occurrence and hybridization with P. quadrifolia occurs very locally, in the San Jacinto Mountains (Buck et al. 2020, 2023).

This is one of the principal species of the piñon-juniper (or P-J) woodlands, one of the most widespread forest types of western North America. In the U.S., the conifers include all of the piñons and at least 6 junipers: Juniperus deppeana, J. flaccida, J. monosperma, J. occidentalis, J. osteosperma, and J. scopulorum. Several other, sometimes rather unusual combinations may occur. At the northern extreme, the Missouri Breaks of eastern Montana have Pinus flexilis-Juniperus scopulorum woodlands, whereas Mexico has many more species of both piñon and juniper that combine in numerous ways. Regardless of its dominant tree species composition, the piñon-juniper woodland is of enormous ecological importance because the dominant trees create a structure that produces habitat diversity, attenuates soil erosion and microclimatic extremes, retains snow cover and enhances soil moisture, supports very high diversity of both cryptogamic and vascular vegetation, and provides an important food source (pine nuts and juniper "berries") for many species of birds, mammals, and insects. These resources are in turn available to humans, who historically have exploited them primarily for grazing domestic animals, and in this connection the piñon-juniper woodland is of great economic importance.

P-J woodlands cover an estimated 19 to 40 million hectares in the U.S., and are also very widespread in Mexico (Gottfried et al. 1995, Romme et al. 2009). They share a semiarid climate, shifting to more continuous forest vegetation at the cool/wet limits of their distribution, and giving way from juniper to shrublands or angiosperm woodlands (such as Cercocarpus sp.) at the hot/dry limits. Romme et al. (2009) broadly summarize the ecology of P-J woodlands by assigning them to three groups. The "persistent woodlands" are found where environmental conditions are favorable for P-J conifers; on these sites, fires have always been infrequent. The "P-J savannas" are found where conditions are suitable for both trees and grasses; such sites are subject to low-severity fire, but little is known about their historical dynamics. Finally, the "wooded shrublands" occur where conditions generally support a shrub community, but trees can increase during moist climatic conditions and periods with little disturbance, and will decrease during droughts and after severe disturbance. All three woodland types are vulnerable to dramatic demographic changes due to varied mechanisms such as recovery from past disturbance, livestock grazing, fire suppression, and climate change. It is clear, though, that the historic record, i.e. observations since the mid-19th century, has documented episodes of both extirpation and regeneration of P-J woodlands affecting a landscape scale, sometimes extending to millions of hectares. Examples include very widespread deforestation due to mining activities in Nevada (Young and Budy 1987, Lanner and Frazier 2011), extensive programs of woodland "control" to enhance profits in the livestock industry (Gottfried and Severson 1994), and a drought in the early 2000s (with accompanying pest and disease-caused mortality) that affected 1.2 million hectares of P-J woodlands and killed up to 350 million piñons in the Four Corners region (Shaw et al. 2005, Hicke and Zeppel 2013, Meddens et al. 2015). All of these considerations are applicable to P. monophylla in particular, except that the Four Corners drought event primarily affected P. edulis; nonetheless substantial drought impacts have afflicted P. monophylla in Nevada (Meddens et al. 2015), with more limited effects observed in other states.

This species, along with Pinus edulis, is host to the dwarf mistletoe Arceuthobium divaricatum (Hawksworth and Wiens 1996). Trees may also be afflicted by insects including the pinyon ips (Ips confusus), pinyon needle scale (Matsucoccus acalyptus), pinyon sawfly (Neodiprion edulicolus) mountain pine beetle (Dendroctonus ponderosae), and the cone predators Eucosma bobana and Dioryctria albovittella (moths). Primary fungal diseases include pinyon blister rust (Cronartium occidentale), singleleaf pine needle cast (Bifusella pini), and black stain root disease (Leptographium [=Verticicladiella] wageneri) (Burns and Honkala 1990, Scharpf 1993).

Both piñons and junipers rely primarily upon birds to disperse their seeds. This is by far the most widespread conifer forest type that relies upon birds, rather than wind, as the primary agent of seed dispersal. Piñons have a singular relationship with the birds that gather, cache and eat their seeds. The trees are completely dependent on these birds for seed dissemination. This relationship is wonderfully detailed in two books by Ron Lanner (Lanner 1981, 1996). Because the seeds are large and wingless, they cannot be disseminated by wind. Instead, the seeds are gathered by four species of corvids: the Clark's nutcracker (Nucifraga columbiana), Steller's jay (Cyanocitta stelleri), Mexican jay (Aphelocoma ultramarina), and pinyon jay (Gymnorhinus cyanocephalus). Each of these will gather and cache huge numbers of seeds for consumption during the winter months. Some seeds are not recovered by the jays, and germinate to produce new seedlings. Steller's and Mexican jays collect seed only from open cones, but pinyon jays and Clark's nutcrackers forage from green cones, and then from open cones as the season progresses. Clark's nutcrackers and Steller's jays probably do not effectively disseminate the seeds because their caches are located in ponderosa pine and mixed conifer forests or in the ecotone above pinyon-juniper woodlands. Mexican jays and pinyon jays, however, cache seeds in woodland areas, the former in small, local territories, whereas the latter transport seeds up to 12 kilometers. Thus, the pinyon jay is the most important of the four species because it forages from both green and mature cones, disseminates the seeds across significant distances, and sites caches in locations where successful regeneration may occur. Pinyon jays can carry an average of up to 56 seeds in an expandable esophagus, and most seeds are cached individually rather than in groups, so there is a good dispersal of the potential seedlings. Pinyon jays live in flocks of 50 to 500 birds, and it has been estimated that during a substantial seed year in New Mexico, about 4.5 million seeds were cached by a single flock (Ronco 1990).

Remarkable Specimens

The largest recorded tree has diameter 135 cm, height 15.2 m, crown spread 15.8 m, and is located in Washoe County, Nevada (American Forests 2008).

The oldest living tree yet found is named MIN-108, discovered in about 2007 by Scotty Strachan and Franco Biondi in the Pilot Range, Nevada, that crossdated to 1106 AD (S. Strachan email 2008.07.13). A few years earlier, Biondi and Strachan found a tree in the Pine Grove Hills of Nevada that crossdated to an age of 888 years (RMTRR 2006).

Ethnobotany

The large, nutritious seeds were a staple food for native Americans living within the range of this species, and are still gathered with enthusiasm. The wood is used primarily for fuel and for fenceposts; in the historic period, the species was widely exploited to fuel railroad locomotives and to produce charcoal for silver smelters (FEIS database). It is also locally harvested for Christmas trees (Burns and Honkala 1990). Young and Budy (1987) provide a detailed description of the charcoal industry as practiced, primarily, in the latter 19th century, before changes in smelting technology eliminated the need for large amounts of charcoal; their data indicate that in at least some cases vast areas were deforested, such as the area within approximately 50 km of the smelters at Eureka, Nevada. Similar deforestation occurred near other mining centers, such as Ely, Nevada, where the Ward Charcoal Ovens are now a state park and national historic site. Areas of P-J woodland were also deforested through wildfires set to improve livestock forage and facilitate movements of domestic sheep (Young and Budy 1987).

The species has been used in a variety of dendrochronology studies, including stable-isotope studies, historical archeology (dating the construction of old mine buildings), air pollution assessment, and a wide variety of climate studies (Bibliography of Dendrochronology). NOAA lists 15 chronologies for this species (NOAA Tree Ring Search Page).

Observations

Easy to find within its range. Piñon-juniper woodlands are particularly widespread and well-developed in east-central Nevada. It is also a reasonably common ornamental, tolerant of relatively wet climates, and can be found in arboreta and larger parks in the eastern U.S. and Great Britain.

Remarks

This was the second species of piñon to be recognized, preceded only by P. cembroides. It was discovered to science on January 24, 1844, in the hills north of modern Bridgeport, California, as related by John C. Frémont (1845): "A man was discovered running towards the camp as we were about to start this morning, who proved to be an Indian of rather advanced age — a sort of forlorn hope, who seemed to have been worked up into the resolution of visiting the strangers who were passing through the country. He seized the hand of the first man he met as he came up, out of breath, and held on, as if to assure himself of protection. He brought with him in a little skin bag a few pounds of the seeds of a pine tree, which to-day we saw for the first time, and which Dr. Torrey has described as a new species, under the name of pinus monophyllus; in popular language, it might be called the nut pine. We purchased them all from him. The nut is oily, of very agreeable flavor, and must be very nutritious, as it constitutes the principal subsistence of the tribes among which we were now travelling."

Singleleaf piñon is the state tree of Nevada (Kral 1993).

Citations

American Forests 2008. The 2008 National Register of Big Trees. Washington, DC: American Forests.

Arno, Stephen F. and Jane Gyer. 1973. Discovering Sierra trees. Yosemite Natural History Association. 89pp.

Buck, Ryan, Sandra Hyasat, Alice Hossfeld, and Lluvia Flores-Rentería. 2020. Patterns of hybridization and cryptic introgression among one- and four-needled pinyon pines. Annals of Botany 126(3):401–11. https://doi.org/10.1093/aob/mcaa045.

Buck, Ryan, Diego Ortega-Del Vecchyo, Catherine Gehring, Rhett Michelson, Dulce Flores-Rentería, Barbara Klein, Amy V. Whipple, and Lluvia Flores-Rentería. 2023. Sequential hybridization may have facilitated ecological transitions in the Southwestern pinyon pine syngameon. New Phytologist 237:2435–49. https://doi.org/10.1111/nph.18543.

Cole, Kenneth. 2003. Map sources for the ranges of one- and two-needled pinyons. http://sbsc.wr.usgs.gov/cprs/research/projects/global_change/RangeMaps/PinyonMapSources.pdf, accessed 2012.04.25, now defunct.

Cole, Kenneth L., Jessica Fisher, Samantha T. Arundel, John Cannella, and Sandra Swift. 2008. Geographical and climatic limits of needle types of one- and two-needled pinyon pines. Journal of Biogeography 35:257-269.

Gernandt, D. L., A. Liston and D. Piñero. 2003. Phylogenetics of Pinus subsections Cembroides and Nelsoniae inferred from cpDNA sequences. Systematic Botany 28(4): 657-673.

Gottfried, G. J., and K. E. Severson. 1994. Managing Pinyon-Juniper Woodlands. Rangelands 16(6):234–236.

Gottfried, G. J., T. W. Swetnam, C. D. Allen, J. L. Betancourt, and A. L. Chung-MacCoubrey. 1995. Pinyon-juniper woodlands. Pp. 95-132 in D. M. Finch and J. A. Tainter (eds.), Ecology, diversity and sustainability of the middle Rio Grande basin. General Technical Report RM-GTR-268. Fort Collins, CO: USDA Forest Service Rocky Mountain Forest and Range Experiment Station.

Hicke, J. A., and Zeppel, M. J. B. 2013. Climate-driven tree mortality: insights from the piñon pine die-off in the United States. New Phytologist 200(2): 301–303. doi:10.1111/nph.12464.

Meddens, A. J. H., Hicke, J. A., Macalady, A. K., Buotte, P. C., Cowles, T. R., and Allen, C. D. 2015. Patterns and causes of observed piñon pine mortality in the southwestern United States. New Phytologist 206(1): 91–97. doi:10.1111/nph.13193.

Montes, José Rubén, Pablo Peláez, Ann Willyard, Alejandra Moreno-Letelier, Daniel Piñero, and David S. Gernandt. 2019. Phylogenetics of Pinus subsection Cembroides Engelm. (Pinaceae) inferred from low-copy nuclear gene sequences. Systematic Botany 44(3):501–518. https://doi.org/10.1600/036364419X15620113920563.

Romme, W. H., C. D. Allen, J. D. Bailey, W. L. Baker, B. T. Bestelmeyer, P. M. Brown, K. S. Eisenhart, M. L. Floyd, D. W. Huffman, B. F. Jacobs, R. F. Miller, E. H. Muldavin, T. W. Swetnam, R. J. Tausch, and P. J. Weisberg. 2009. Historical and modern disturbance regimes, stand structures, and landscape dynamics in piñon-juniper vegetation of the western United States. Rangeland Ecology and Management 62:203-222.

Ronco, Frank. 1990. Pinyon, in Burns and Honkala (1990).

Shaw, J. D., B. E. Steed, and L. T. DeBlander. 2005. Forest Inventory and Analysis (FIA) annual inventory answers the question: What is happening to pinyon-juniper woodlands? Journal of Forestry: 6:280-285.

Torrey, J., and J. C. Frémont. 1845. Descriptions of some genera and species of plants, collected in Captain J. C. Frémont's exploring expedition to Oregon and North California, in the years 1843-1844 (p. 319). Available: Biodiversity Heritage Library, accessed 2023.03.10.

Young, J. A., and J. D. Budy. 1987. Energy crisis in 19th century Great Basin woodlands. In Proceedings - pinyon-juniper conference; 1986 January 13-16; Reno, NV. Edited by R. L. Everett. U.S. Department of Agriculture, Forest Service, Intermountain Research Station, Ogden, UT. doi:10.2737/INT-GTR-215.