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Conservation status
(as P. cembroides)

Pinus discolor

Bailey et Hawksworth 1979

Common names

Border piñon (Lanner 1981).

Taxonomic notes

Subsection Cembroides. Syn: P. cembroides subsp. cembroides var. bicolor Little 1968; P. culminicola var. discolor (Bailey and Hawksworth) Silba 1985 (Farjon & Styles 1997).

The validity of this taxon is greatly disputed. At one extreme, Kral (1993) summarily dismisses its existence altogether, and Farjon and Styles (1997) regard it, combined with P. johannis Robert-Passini, as merely a variety of P. cembroides (var. bicolor Little) while at the other extreme, Perry (1991) and Price et al. (1998) regard it as a valid species distinct in its own right. An intermediate view is taken by Passini (1994), who treats P. discolor as a synonym of P. johannis. It is clearly very close to that species but does differ slightly, and might best be treated as a variety of it, but the combination Pinus johannis var. bicolor has not yet been published.

There have been no reports of any natural hybridization with P. cembroides, despite frequent intermingled occurrence, which strongly supports specific distinction from P. cembroides. Pending further research, it is retained as a species here.

The view of Silba (1985) that it and P. johannis are varieties of P. culminicola has some merit in showing that they are more closely related to P. culminicola than to P. cembroides (a fact subsequently demonstrated by Malusa (1992)), but is not widely followed.

Description

Small tree to 15 m tall, multi-stemmed, rarely with a single trunk. Crown low, dense and rounded, spreading, with branches extending outward as much as 3-4 m. Bark in young trees smooth and gray; in older trees rough and scaly, but not deeply furrowed or ridged. Twigs dark gray, rough, the bases of the leaf bracts somewhat decurrent. Leaves (2-)3(-4) per fascicle, 3-5 cm long, 0.9-1.2 mm thick; flexible, margins entire, stomata present only on the ventral surfaces, with a distinctive variegated appearance because the dorsal surface is dark green and the ventral surfaces glaucous white. Resin canals 2, external, dorsal; vascular bundle single. Fascicle sheaths orange-brown, 3 mm long, fading gray, and curled backward into a rosette; later occasionally deciduous. Cotyledons (6-)9(-11). Seed cones in first year brown, 9-11 × 5-7 mm, borne singly or in pairs on short slender peduncles. Cones at maturity orange-brown, resinous, oblong, up to 3.5 × 2-3 cm when closed, 4-5.5 cm wide when open, opening at maturity and soon deciduous. The peduncle is 3-4 mm long, falling with the cone. Cone scales are slightly glossy, thin and stiff, the apophyses irregularly rhomboid, small, thin, flat, 10-15 mm wide, with a weak transverse ridge; umbo dorsal, depressed, the prickle minute and soon deciduous. Only the central (3-)8-15 scales are seed-bearing, those at the base and apex of the cone generally very small and sterile. Seeds dark orange-brown with a rudimentary 0.5-1 mm wing that remains in the cone after seed release; about 10-12 × 10 mm, the seed coat or shell 0.5-1.0 mm thick, hard; about 2,200 seeds/kg; endosperm white; edible. Wood pale yellowish brown, used only for fuel (based on Perry 1991 description of P. johannis modified per M.P. Frankis).

The taxon is extremely similar to P. johannis. Some of the few differences (in stature, cone size, and seed size) are based on small sample sizes, and may prove inconclusive with further research. Differences in turpene composition have also been reported (Zavarin and Snajberk 1986), but the validity of this research has been questioned (Farjon and Styles 1997).

Distribution and Ecology

S Arizona & New Mexico. Notably, the eastern Mogollon Rim, Kitt Pk. and the Santa Catalina Mtns (Jeff Bisbee email 2013.11.17, Lanner 1981). Mexico: Sonora, Chihuahua and Durango at 1500-2400 m (Perry 1991). Hardy to Zone 8 (cold hardiness limit between -12.1°C and -6.7°C) (Bannister and Neuner 2001).

Big tree

Oldest

Dendrochronology

Ethnobotany

Potentially a valuable slow-growing ornamental species for small gardens in drought-prone areas, but it is scarcely in cultivation yet. USDA hardiness zone 8.

Observations

Jeff Bisbee (email 2013.11.17) reports that it occurs north of Clifton, AZ along Highway 191. "It very interesting because P. monophylla fallax is growing with it, some trees having entirely single needles, and the typical larger cones of monophylla with thicker cone scales and apophysis. These contrast with the very small, thin-scaled cones of discolor and the bi-colored needles. Intermixed with these two pinyon pines are also many two needled pinyons, which also have the larger cones. Some of them appeared to have somewhat bi-colored needles, others were more like edulis with evenly distributed stomata. Farther up the rim, were good edulis. So three pinyon pines in a small area." The same area has Cupressus arizonica, and at somewhat higher elevations along the highway are populations of P. reflexa, P. ponderosa, Picea engelmanii, and Picea pungens.

Remarks

This species is one of the principal hosts for the dwarf mistletoes Arceuthobium pendens (Hawksworth and Wiens 1996).

Citations

Bailey, D. K. and F. G. Hawksworth. 1979. Pinyons of the Chihuahuan Desert region. Phytologia 44:129-133. Available: www.biodiversitylibrary.org/item/47046, accessed 2011.05.21.

Zavarin, E. and K. Snajberk. 1986. Monoterpenoid differentiation in relation to the morphology of Pinus discolor and Pinus johannis. Biochemical Systematics and Ecology 14: 1-11.

Much of this page was prepared by M.P. Frankis, 1999.02.

See also

Last Modified 2013-12-07