Pinus culminicola description

Pinus culminicola Andresen & Beaman 1961

Common Names

Potosí piñon (2).

Taxonomic notes

Malusa (1) showed this pinyon to be closely related to P. johannis and P. discolor, all of which share similar bark and leaf stomatal distribution, with P. quadrifolia also allied but less closely so. P. orizabensis (not examined by Malusa) also belongs to this group. Silba (3) reduced P. johannis and P. discolor to varieties of P. culminicola, but this is questionable; for instance, there is no evidence of hybridisation where P. johannis and P. culminicola are sympatric (see under P. johannis).

Description

A shrub or small tree 1-5 m tall and up to 15-20 cm dbh, commonly (if not invariably) multistemmed from the base, usually spreading with branches extending outward from the base for 3-4 m. The crown is low, dense and rounded. The bark is scaly, with peeling shaggy grey-brown plates exfoliating to expose fresh bright orange bark beneath, (similar to P. johannis); bark on young stems smooth and grey. Shoots dark grey, rough; the bases of the leaf bracts somewhat decurrent. Leaves five in a fascicle, 3-5 cm long, 1-1.3 mm thick; stiff, curved toward the shoot apex, margins entire, stomata present only on the ventral surfaces, the dorsal surface dark green and the ventral surface glaucous white. Fascicle sheaths orange-brown, 3 mm long, fading grey-brown and curling backward into a rosette. Seed cones are sessile or on a 1 mm peduncle, 2.5-4.2 cm long, globose, opening obtriangular (broad flat base, with a ± pointed apex), to 3.5-5.5 cm wide, very resinous, opening at maturity and soon deciduous. The scales are thin, coarsely wrinkled, matte, orange-brown, the apophysis rhomboid with a pointed apex, 10-15 mm broad, with a 4-5 mm wide blackish umbo, flat or slightly raised. Fully developed cones in the upper crown have 10-15 fertile scales; small cones from low branches (with poor pollination and nutrient supply) are often lopsided with 1-10 fertile scales. Seeds dark orange-brown, about 10-12 mm long and 10 mm wide, with a rudimentary 0.5-1mm wing that remains in the cone on seed release; the seed shell 0.5-1.0 mm thick, hard; endosperm white. Most seed is dispersed by mid-November, suggesting cone maturity in late October. (compiled from 3, 6).

Range

Mexico: A large colony grows in the summit area of Cerro Potosí in Nuevo León, 65 km W of Linares at 24°52'N 100°14'W, with three or four small and rather inaccessible colonies on the high ridges about 50 km northwest of there on the Nuevo León-Coahuila border; see (5) for details. A high altitude species, found at (3000)3300-3700 m - the highest mean altitude for any pine.

Big Tree

Best growth, to 4(5) m tall, is at around 3400-3450 m on Cerro Potosí; plants near the summit are shorter, mostly 1-1.5 m tall (6).

Oldest

Dendrochronology

Ethnobotany

Perhaps the only piñon with no history of aboriginal use, as it grows at formerly uninhabited altitudes. Like the other piñons, it has edible seeds and no doubt the microwave station staff on Cerro Potosí now collect them for local use on occasion.

USDA hardiness zone 7. With its very attractive blue-green foliage, it is potentially a valuable slow-growing ornamental species for small gardens in cool dry areas, but it is still very rare in cultivation.

Observations

It is very easy to see on the top of Cerro Potosí, being the dominant species from 3300 m up to a few metres short of the summit (3670-3713 m, depending on which map you use!). There is a steep dirt road of not-too-dreadful condition that zig-zags up the NE slopes right to the top, where it serves a microwave station. This station is on the highest point, where it has obliterated most of the small alpine 'bald' that used to exist above the Pinus culminicola treeline. See Perry (3) for directions to this road and advice on travel.

Remarks

In November 1991, after a hot dry two years in 1989-1990, the summit trees had a heavy cone crop of well-formed large (4cm) cones, but lower trees had poorer crops of mostly somewhat smaller cones, presumably due to drought stress. In normal years, the reverse probably applies with conditions at the summit too cool for good crops. The seeds are sought out and dispersed by Gray-breasted Jays and Clark's Nutcrackers, which spread the seeds widely, hiding them in the ground for a winter food resource; as they hide more than they need, the surplus are left to germinate safe from marauding rodents (2).

Citations

(1) Malusa 1992.
(2) Lanner 1981.
(3) Perry 1991.
(4) Silba 1985.
(5) D.H. Riskind and T.F. Patterson. 1975. Distributional and ecological notes on Pinus culminicola. Madroño 23: 159-161.
(6) M.P. Frankis, field notes, November 1991.