Picea engelmannii subsp. mexicana
Mexican spruce, Pícea mexicana [Spanish].
Although often cited as a variety (Taylor and Patterson 1980, Taylor et al. 1994), the substantial difference in climatic adaptation (USDA zone 7, vs. 3-4 in the type), and chemical similarities to P. sitchensis (Taylor et al. 1994) justify the treatment at subspecies rank as proposed by Schmidt (1988). There is also merit in awarding it species rank, as did Ledig et al. (2004), but it would still be recognized as sister to P. engelmannii.
"This ssp. differs from the typical ssp. in its lighter (grey) bark, its narrower leaves (1-1.2 mm) and its narrower and slightly longer bract scales (4-6 mm)" (Farjon 1990). The bract scale measurement is not wholly reliable, as equally long bracts can be found on the typical subspecies, but the cones can be distinguished by their larger mean size (4.5-8 cm, vs. 3-6cm in the type) and slightly larger seed scales, but there is much overlap (cones in collection of M. P. Frankis); see also Taylor et al. (1994).
Mexico: First found in the Sierra de la Marta, 75 km SE of Saltillo in Nuevo Leon, NE Mexico. It grows on steep, moist, north-facing slopes on soils derived from dolomite, at 3000-3400 m elevation (Farjon 1990). Another population on Cerro Mohinora in S Chihuahua, discussed as uncertain by Taylor and Patterson (1980), has now been assigned to ssp. mexicana (Farjon 1990, Taylor et al. 1994). A third population has been found in the Sierra el Coahuilon, Coahuila. USA: The population of Picea engelmannii in the Chiricahua Mts of Arizona has in the past been referred to this subspecies (Taylor and Patterson 1980: p.438), but molecular analyses presented by Ledig et al. (2004) indicate those trees belong to the type subspecies. USDA hardiness zone 7.
This species (under the name Picea mexicana) is listed as endangered in Mexico under NOM-ECOL-059-94. Although each of the three populations probably contains several thousand trees (Ledig et al. 2000), they are nonetheless widely disjunct and grow on some of the tallest mountains in the region. This taxon warrants treatment as one of the most critically endangered conifers in the world, at high risk of extinction in the foreseeable future due to stressors including climate change and fire.
Ledig, F.T., M. Mápula-Larreta, B. Bermejo-Velazquez, V. Reyes-Hernandez, C. Flores-Lopez, and M.A. Capo-Arteaga. 2000. Locations of endangered spruce populations in Mexico and the demography of Picea chihuahuana. Madroño 47(2):71-78.
Ledig, F.T., P.D. Hodgkiss, K.V. Krutovskii, D.B. Neale, and T. Eguiluz-Piedra. 2004. Relationships among the Spruces (Picea, Pinaceae) of Southwestern North America. Systematic Botany 29(2):275-295.
Taylor, R.J., and T.F. Patterson. 1980. Biosystematics of Mexican spruce species and populations. Taxon 29 (4): 421-469.
This page co-edited with Michael P. Frankis, 1998.12.
The species account at Threatened Conifers of the World.
Last Modified 2017-11-12