Parry piñon, four-leaved nut pine, Sierra Juárez piñon.
Subsection Cembroides (Perry 1991). Synonymy:
San Diego County in California, and adjacent Baja California Norte, are home to two piñon pines that introgressively hybridize within this range. One of them is the singleleaf piñon, Pinus monophylla, a very distinctive and widespread species with the northwesternmost distributon of all the piñons. The other is a distinctive and widespread 5-needle piñon of Baja California Norte, reaching its greatest abundance in the Sierra Juárez. It has been called Pinus quadrifolia and P. juarezensis, but both taxa were unfortunately described because their type specimens come from a zone of introgression between the 5-needle pine and P. monophylla. Thus the 5-needle pine has never really been described, and must be tagged either P. quadrifolia or P. juarezensis. The former name was assigned earlier, so the latter name is here reduced to synonymy. Someday, somebody should really take one of the Sierra Juárez pines and describe it as a variety, but until then we shall have to content ourselves with a 5-needle pine named P. quadrifolia.
The trouble all started in 1850 when C.C. Parry, as part of the United States and Mexican Boundary Survey (page 208-9; Plate LIII), collected this species in the "mountains east of San Diego," presumably the Laguna Mountains. This is an area of active hybridization between the two piñons and many trees bear 4-needled fascicles, thus the epithet quadrifolia. When P. juarezensis was described by Lanner (1974a, 1974b, 1981), he segregated it as a 5-needle piñon endemic to the Sierra Juárez of Baja California Norte and extreme southern California, reducing P. quadrifolia to hybrid status as P. × quadrifolia Parl. Farjon and Styles (1997), the other principal authorities to examine this issue, regard P. juarezensis as a synonym for P. quadrifolia, discounting the idea that because P. quadrifolia displays characters intermediate between P. monophylla and P. juarezensis it must then be a hybrid. I must disagree. Lanner describes some populations of P. juarezensis -- such as one atop the Laguna Mountains -- that do not display hybrid characters. I have seen this tree on the southern Mt. San Jacinto massif (March 2004), on the Laguna Mountains, at Lanner's P. juarezensis type locality in northern Baja California, and in many areas from there south to the Laguna Hanson area of Baja California Norte (March 2001). I had the opportunity to examine trees in many ecological settings, some of which were shared by P. monophylla and others not. Fully developed sun foliage had fewer than 5 needles per fascicle primarily at sites where P. monophylla was also present. A particularly good example was found on the southern Mt. San Jacinto massif, along CA highway 371 about 1 mile south of its junction with CA highway 74, where I found a large pine with almost all 2-needle fascicles, showing leaf and cone characters intermediate between Lanner's P. juarezensis and P. monophylla, both of which were growing in the vicinity. I have prepared details with photos of the hybrids. Also, at the P. juarezensis type locality near La Rumorosa in Baja California, it grows in a mixed stand with P. monophylla, and many of the trees have a high density of fascicles with fewer than 5 needles. The type locality stand is much drier and more open than the species' usual habitat, is not a good example of the 5-needle piñon of northern Baja, and I believe that the type specimen of P. juarezensis has been affected by introgression.
In fairness, I should add that Lanner, Farjon, Styles and I have all assessed introgression by observation of field and herbarium material. To the best of my knowledge, no one has used terpene or molecular data to examine the question.
In conclusion, I believe that there is an ecologically important 5-needle piñon in Baja Calfornia Norte that has not been described as a species, but is close to P. juarezensis. There may or may not be a rare 4-needle piñon in San Diego County that was described as P. quadrifolia, and given the current skimpy data we cannot determine with confidence whether it had a hybrid origin. The simplest solution from the standpoint of taxonomic nomenclature is to reduce P. quadrifolia to a variety of P. juarezensis, but the name "P. juarezensis var. quadrifolia" has never been published. Until that happens, P. juarezensis and P. quadrifolia are probably best regarded as synonyms, of which P. quadrifolia was first published. We must live with the unfortunate consequence that 99% of all P. quadrifolia trees have 5-needle fascicles.
P. quadrifolia was widely regarded as a good species when a stand of it was planted in the native plant garden at the Rancho Santa Ana Botanical Garden in Claremont, California. I wondered how diligently they must have searched to find so many 4-needle trees. The trees have done very well in Claremont, so much so that they now form a stand as dense and dark as any thicket, virtually devoid of an understory. The offspring of these trees, if they all bore 4-needled fascicles, could contest the hybrid origin of the species; but though I searched, I could find no seedlings or saplings, nor any evidence of viable seed.
Trees 5-9(-15)m tall and up to 50cm dbh. Round, fairly straight single trunk, much branched within the crown which is dense and narrowly pyramidal in young trees, with age becoming irregularly rounded. Bark at first light gray and smooth, with age becoming red-brown, thick, scaly, longitudinally and horizontally furrowed. Branchlets slender, pale orange-brown, puberulent-glandular, aging brown to gray-brown; pulvini not decurrent. Buds ovoid, light red-brown, ca. 0.4-0.5 cm, slightly resinous. Leaves in fascicles of (4-)5, usually connate the first year, slightly curved, 1.5-6 cm × 1-1.7 mm, stiff, sharp, green to blue-green, margins entire, finely serrulate, apex subulate, adaxial surfaces mostly strongly whitened with stomatal bands, resin canals (1-)2(-3), dorsal; fibrovascular bundle single; leaves persisting 3-4 years. Fascicle sheath 5-9 mm long, curling into rosettes, later deciduous. Pollen cones ovoid, ca. 10 mm, yellowish. First-year cones borne singly and in pairs on slender, short peduncles; globose with thick, transversely keeled scales. Second-year cones mature subglobose, symmetrical; (3-)4-10(-10) cm long when open, pale yellow-brown, soon deciduous when mature, the peduncle very small and falling with the cone. Cone scales few, only the central scales seed-bearing; apophysis rhomboidal, strongly raised, transversely keeled; the umbo dorsal, flat to depressed, bearing a minute early deciduous prickle. Seeds brown, wingless, 14-17 × 6-8 mm; seed coat 0.2-0.3 mm thick; endosperm white (Little 1980, Perry 1991, Kral 1993).
US: S California and Mexico: Baja California Norte; distributed in mountains from the southern San Jacinto massif to the Sierra San Pedro Mártir. Habitat is semi-arid to arid foothills and mesas at altitudes ranging from 1,100 to 2,000 m. Rainfall at the lower elevations generally does not exceed 500 mm annually and temperatures may drop to freezing during the winter months. At the higher altitudes (1,600-2,000 m) frosts often occur during the winter and annual rainfall may reach 600 mm with about 30% occurring in the form of snow and sleet" (Perry 1991). Hardy to Zone 8 (cold hardiness limit between -12.1°C and -6.7°C) (Bannister and Neuner 2001). See also Thompson et al. (1999).
My field observations suggest that P. quadrifolia grows in a variety of forest formations depending on available moisture. At the mesic end of the scale, it occurs as an understory tree and on locally droughty sites within Pinus jeffreyi forests having canopy closure less than 67%. As site moisture decreases, P. jeffreyi is increasingly restricted to riparian areas and then is excluded completely. At these moisture levels, P. quadrifolia forms continuous stands of tens to thousands of individuals, sometimes with crown closure as high as 90%. On still more xeric sites, crown closure is lost and P. monophylla becomes an increasingly important component of the stand, as does Juniperus californica and various nonconiferous chaparral shrubs such as manzanitas (Arctostaphylos sp.). On the driest sites, P. quadrifolia disappears, leaving a P. monophylla--J. californica stand. I suspect that fire is an important determinant of stand dynamics on sites with potentially high canopy closure, simply because such settings develop fuel loadings sufficient to carry a fire and the nonconiferous component is dominated by chaparral, a characteristic fire-dominated community. Within the historical era, stand dynamics have also been modified by forest clearing to increase available forage for cattle.
Diameter 70 cm, height 16 m, crown spread 13 m. Locality: Riverside County, CA (American Forests 1996).
No data, except that I have counted rings on a few stumps and found nothing exceeding 200 years. Twice that age would not be surprising.
The seeds are "sold on the market as pine nuts along with the seeds of P. edulis and P. monophylla ... Like most of the nut pines, the trunk is short and small in diameter and thus hardly useful for sawn lumber. However, it is used locally for posts and firewood" (Perry 1991).
This is an extremely common pine in the Sierra Juárez of Baja California Norte. A drive south from Mexico Highway 2 to the Parque Nacional Constitución de 1857 will take you through many kilometers of groves, and it is a common understory species at the park. It can also be seen in a pure stand near the radio transmitters at the summit of the Laguna Mountains east of San Diego. You may find these locations useful:
Nice mixed stand (with P. monophylla) at 32.3018°N, 115.9371°W.
Growing with a minor component of P. jeffreyi at 32.2026°N, 115.9360°W.
Dense single-species stand with lots of seedlings at 32.1883°N, 115.9277°W.
"The rather large, thin-shelled seeds are gathered for food by birds and rodents" (Perry 1991).
Sudworth, G. B. 1897. Nomenclature of the arborescent flora of the U.S. U.S.D.A. Division of Forestry Bulletin. 14:17.
Last Modified 2014-12-13