Pinus yecorensis (Yecora pine) description

Pinus yecorensis

Debreczy et I. Rácz 1995

Common names

Yecora pine, piño colorado. piño rojo (Felger et al. 2001).

Taxonomic notes

Syn.: Pinus pseudostrobus Lindl. subsp. yecorensis (Debreczy et I. Rácz) Silba 2009. Type collection southeast Sonora near Yecora, 1800 m, 1994.05.09; Debreczy, Rácz, Biró, et al. 39798 (holotype BP, isotypes A, CHAP, E, MEXU, NA).

Surprisingly, some authorities still doubt the validity of this taxon, which is why it has not been assessed for conservation concern. Farjon and Styles (1997) placed it into synonymy with Pinus pseudostrobus var. pseudostrobus and its morphological characters appear to fall fully within the range of variability in that taxon. However, its occurence is more northerly than that of P. pseudostrobus and its ecological setting, in woodlands below the elevation of continuous forest, is somewhat distinct. An analysis by Zeb et al. (2020), comparing the complete chloroplast genomes of 97 Pinus taxa, placed P. yecorensis sister to a clade containing all other species in subg. Pinus, a surprising and unexplained result that could indicate an usual event this species' evolutionary history. However, multiple studies have consistently established a close relationship between P. yecorensis, P. douglasiana and P. maximinoi:

Felger et al. (2001) who allied P. yecorensis with P. douglasiana on purely morphological grounds.
Gernandt et al. (2009) used chloroplast DNA to placed P. yecorensis in a clade with P. douglasiana and P. maximinoi.
Hernández-León et al. (2013) used plastid DNA markers to assess all species in Pinus section Trifoliae and placed P. yecorensis sister to P. douglasiana and P. maximinoi.

See the "Taxonomic notes" for Pinus ponderosa for discussion of relationships within subsection Ponderosae; briefly, a variety of molecular studies have confirmed the status of P. yecorensis as a distinct taxon.

There is one described variety, P. yecorensis Debreczy et A. Racz var. sinaloensis Debreczy et I. Rácz 1995.

Description

Trees to 30 m tall and 95 cm dbh, at maturity with a spreading, dome-shaped crown. Bark red-brown, rough, with dark longitudinal furrows. Twigs >10 mm thick, scaly, initially glaucous. Leaves (4-)5(-6) per fascicle, ca. 1 mm thick and 20-35(-38) cm long, slightly drooping. Fascicle sheaths dark, persistent. Seed cones pendent, subsessile or on a thick peduncle up to 15 mm long, woody, 5-15.5 cm long, symmetric to slightly asymmetrical, somewhat or variably persistent, peduncle falling with the cone or sometimes not, remaining on the tree with a few basal scales. Cone scales stout, apophysis moderately to very thickened, umbo dorsal (downward-pointing) with a small prickle. Seeds ovoid, 6.0-8.4 mm long with a broad 16-25 mm wing. Pollen shed March-April (Felger et al. 2001).

Compared to P. engelmannii, P. yecorensis has a denser crown, usually more slender twigs, and brighter green, thinner leaves with five (not 3) leaves per fascicle. Compared to P. arizonica, it has darker, rough bark; thicker twigs; longer, more drooping leaves; larger, heavier cones; thicker cone scale tips; and blunt prickles. Compared to P. oocarpa, it has longer and slightly thinner, more drooping leaves; larger seed cones; and scales with thicker tips and lacks evidence of a conspicuous black band on the inner surface (Felger et al. 2001).

Distribution and Ecology

Mexico: Sonora, Chihuahua, Sinaloa, Durango; on the Pacific slopes of the Sierra Madre Occidental at 900-1975 m elevation, mainly in woodlands with Quercus spp. and Pinus spp., including P. oocarpa, P. leiophylla subsp. chihuahuana and P. engelmannii; often it is lower than any other pines. In one area it grows at elevations as low as 900 m on hydrothermal soils in a landscape otherwise dominated by tropical deciduous forest; otherwise it has not been recorded below 1200 m elevation (Felger et al. 2001).

Distribution data from the Intermountain Region Herbarium Network, accessed 2012.11.22 (check in 2021 revealed no new specimens).

The IUCN does not recognize this species and no conservation assessment has been performed. In their description of the species, Debreczy and Rácz (1995) state "the tree seems to be restricted to the localized sites and protection of some populations should be considered." Few collections have been recorded, further supporting the idea that this is a species of conservation concern, particularly as it is vulnerable to logging.

Remarkable Specimens

None recorded as of 2023.02.

Ethnobotany

Exploited for lumber (Felger et al. 2001).

Observations

See the distribution map.

Remarks

The epithet yecorensis comes from the town of Yécora in Sonora, near which the species was discovered.

Citations

Debreczy, Z. and I. Rácz. 1995. New species and varieties of conifers from Mexico. Phytologia 78(4):217. Available at the Biodiversity Heritage Library, accessed 2012.11.22.

Felger, R.S., M.B. Johnson, and M.F. Wilson. 2001. The trees of Sonora, Mexico. Oxford: Oxford University Press. ISBN 0-19-512891-5.

Gernandt, D.S., S. Hernández-León, E. Salgado-Hernández, and J.A. Pérez de la Rosa. 2009. Phylogenetic relationships of Pinus subsection Ponderosae inferred from rapidly evolving cpDNA regions. Systematic Botany 34:481-491.

Hernández-León, S., D. S. Gernandt, J. A. Pérez de la Rosa, and L. Jardón-Barbolla. 2013. Phylogenetic relationships and species delimitation in Pinus section Trifoliae inferred from plastid DNA. PLoS ONE 8(7): e70501. doi:10.1371/journal.pone.0070501.

Zeb, U., W. Dong, T. Zhang, R. Wang, K. Shahzad, X. Ma, and Z. Li. 2020. Comparative plastid genomics of Pinus species: Insights into sequence variations and phylogenetic relationships. J. Syst. Evol. 58(2): 118–132. doi:10.1111/jse.12492.