Pinus rzedowskii (pino de Rzedowski) description

Pinus rzedowskii

Madrigal Sánchez et Caballero Deloya 1969

Common names

Pino de Rzedowski, Pino, ocote [Spanish].

Taxonomic notes

This unusual species, although usually classified with the piñon pines in subgenus Strobus section Cembroides, contains certain characters expected in subgenus Pinus. It has a relatively high level of genetic variation, compared to most conifers, but with considerable inbreeding in each of the populations, and evidence of a substantially larger population size in the (evolutionarily) recent past (Delgado et al. 1999).

Description

A tree (15-)20-25(-30) m tall and 30-60 cm dbh, trunk straight or curved, often branching low. Young trees are pyramidal with branches regularly spaced whorls, but at maturity the crown is generally open and irregularly branched. Bark on young trees is thin, smooth, grayish green, turning scaly, flaking, red-brown, and still later turning thick and rough with deep horizontal and longitudinal fissures dividing the bark into rectangular plates that are rough, scaly and dark brown. Branchlets are slender, gray, smooth. Bases of the leaf bracts are not decurrent; the needles are borne along the entire branchlet, persisting 2-3 years. Needles are flexible, slender, in groups of (3-)4-5, 6-10 cm long and 0.6-0.8 mm wide, the edges finely serrate; stomata on the two inner surfaces only; resin canals 2-3, occasionally 4, external on the dorsal surface with occasionally 1 external on a ventral surface; fibrovascular bundle single. The fascicle sheaths form a rosette of recurved scales and are later deciduous. Young cones are erect on peduncles 1.5-2.0 cm long, with thick, wide, recurved scales. Mature cones are oblong, tapering slightly, symmetrical, pendent, borne singly and in whorls of 2-4; 10-15 cm long and 6-9 cm wide when open; yellowish brown to lustrous ochre color when mature, ripening in the fall and soon deciduous; the peduncle slender, curved, 1.5-3.0 cm long, falling with the cone. There are 80-120 cone scales that are 15-22 mm wide; the apophysis is subpyramidal with a prominent, horizontal keel, the apex acutely angled; the umbo is dorsal, small, dark brown, depressed, with a very small, downward-curved prickle. The apophyses and the umbo usually bear a small drop of clear amber resin. The dark brown seeds are (6-)8(-10) mm long and (4-)5-6 mm wide with an articulate wing 20-30(-35) mm long and 8-13 mm wide. Cotyledons 9-14, mostly 10, 11 and 12. The wood is moderately hard, the heartwood lustrous pale brown, sapwood creamy white, not very resinous (Perry 1991, Farjon and Styles 1997).

Distribution and Ecology

Mexico: Michoacán: at (1710-)2100-2480 m elevation in the Sierra Madre del Sur, District of Coalcomán, in three disjunct localities, one near the village of Dos Aguas and the others approximately 40 km to the W: Cerro de Chiqueritas, Cerro Ocotoso, and Puerto del Pinabete.. Each location has from 1 to 4,000 trees, with the species as a whole comprised of 12 populations totalling 6,000 to 6,500 trees (Delgado et al. 1999).

All populations "occur on steep, very rocky limestone soils; ... rainfall in the area is estimated to be 1,500 mm annually, almost all occurring during the period June-October; temperature is estimated to range from a minimum of -5°C to a maximum of 30°C in April just prior to the rainy season. On the best site, Puerto del Pinabete, the species was associated with P. pseudostrobus, P. herrerai, P. michoacana and P. oocarpa. At Cerro Chiqueritas and Cerro Octoso, both very rocky sites, no other pines were found with the small populations of P. rzedowskii" (Perry 1991).

Zone 10 (cold hardiness limit between -1°C and +4.4°C) (Bannister and Neuner 2001).

Remarkable Specimens

Delgado (1997, cited by Delgado et al. 1999) reports trees up to 120 cm dbh and up to 50 m tall.

Ethnobotany

Observations

"From Mexico City drive due west on Highway 15 to Morelia, capital of Michoacán State. At Morelia continue west to the city of Uruapan; at Uruapan turn south on Highway 37 to the small town of Nueva Italia. There turn west again to the town of Apatzingan, then go south again to the village of Aguililla. From Aguililla a narrow dirt road leads westward to the village of Dos Aguas. There a guide will be needed in order to locate the small, isolated stands of P. rzedowskii. The trip to Dos Aguas should be undertaken only during the dry season (November-March) and only in a vehicle with high clearance" (Perry 1991).

Burkhard Witt (email 2006.08.31) reports "in February 2000 I traveled to the village Dos Aguas (half ghost timber-town) to see Pinus rzedowskii. ... I found about 15 more or less young mature trees and about 5 young plants, growing together with cacti and agave. The highest trees were about 8 to 10 m tall. All were bearing numbers on their stem, so I think there is some investigation about this species (see Delgado et al. 1999). On the rocky summit, like Perry wrote, Pinus rzedowskii was the only pine species. But only 30 m below the summit is the border with a forest which consists for example of Pinus herrerae, P. pseudostrobus and P. oocarpa with epiphytic tillandsias and some orchids. Here the site is not so steep and rocky and I found no more specimens of Pinus rzedowskii.

Remarks

The epithet honors Jerzy Rzedowski Rotter (b. 1926), eminent Mexican botanist.

P. rzedowskii "possesses many characters that are commonly associated with either one or the other of the two Pinus subgenera, Pinus and Strobus, but it has been assigned to subgen. Strobus. Its foliar morphology and anatomy, as well as preliminary cpDNA (chloroplast DNA) analyses, place it with P. cembroides in a highly distinct but as yet unresolved clade distant from other haploxylon pines. However, the bark, seed cones and seeds bear a close resemblance to certain species in subgen. Pinus, and indeed its small seeds with large wings render it anomalous with regard to all of the other Piñon pines, which have large wingless seeds. Farjon and Styles (1997) attribute these characters, and in particular the development of small winged seeds, as perhaps reflective of convergent evolution; perhaps P. rzedowskii represents a piñon that has evolved away from dependence on animal vectors for seed dispersal (see P. albicaulis for more on animal dispersal of wingless pine seeds).

The three small groups of pines in Michoacán are the only known populations in Mexico. Only one other Mexican pine is more rare and endangered viz. P. maximartinezii (Perry 1991). Perry notes that "In all three small groups of pines totaling ca. 30 ha, most of the mature trees had large fire scars and many trees were dead - evidence of repeated ground fires. In addition very little reproduction was noted, and it was difficult to find young trees under 12 cm in diameter. It is entirely possible then, that during the long dry season, this species could be wiped out completely by a severe fire" (Perry 1991). The pine has not received formal protection in its native habitat (Farjon and Styles 1997).

Citations

Delgado, V. P. 1997. Estructura genética y demográfica de una especie del género Pinus (Pinus rzedowskii) endémica de Michoacán, México. Master’s thesis, Universidad Nacional Autónoma de México. México D.F.

Delgado, P., D. Piñero, A. Chaos, N. Perez-Nasser, and E. R. Alvarez-Buylla. 1999. High population differentiation and genetic variation in the endangered Mexican pine Pinus rzedowskii (Pinaceae). American Journal of Botany 86(5):669-676.

Madrigal, S. X., and M. C. Deloya. 1969. Una nueva especie mexicana de Pinus. Boletín Técnico del Instituto Nacional de Investigaciones Forestales Number 26. México D.F.