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Scientific name: Picea engelmannii subsp. mexicana (Martínez) P. A. Schmidt 1988
Synonyms: Picea engelmannii var. mexicana (Martínez) Silba, Picea engelmannii var. mexicana R.J. Taylor & T. F. Patterson, Picea engelmannii var. mohinorsensis Silba, Picea engelmannii subsp. mohinorsensis (Silba) Silba, Picea mexicana Martínez
Common names: Mexican spruce
Trees to 40-45(-50) m tall, d.b.h. to 1- 1.5(-2) m. Trunk monopodial, this subspecies differs from the typical subspecies in its lighter (grey) bark. Branches of first order short, slender, spreading horizontally, curved upward at ends, lower branches more pendant. Branches of second order short, dense, spreading or pendulous, crown narrowly conical or narrowly columnar. Branchlets slender, firm, becoming pendulous, greenish yellow at first, soon yellowish brown, ridged and grooved, finely pubescent when young. Vegetative buds ovoid-conical, 5-6 mm long, resinous at apex, bud scales obtuse-triangular, appressed, apices later spreading, red brown, persisting several years. Leaves spreading radially, crowded above leading shoots, directed forward, (1.2-)1.5-2.5 cm long, 1-1.2 mm wide, and the bract scales are slightly longer (4-6 mm long, vs. 3-5 mm), leaf colour glaucous green. Pollen cones axillary, 1-1.5 cm long, yellowish. Seed cones terminal, erect at first, pendulous at maturity, sessile, ovoid-cylindric, apex obtuse, (2.5-)3-6(-7.5) cm long, 2-2.5(-3.5) cm wide with opened scales. Colour (immature) green tinged with red, maturing to light reddish brown or pale yellowish brown. Seed scales obovate-obtrullate, thin and flexible, 1.2-1.5 × 0.9-1.2 cm at mid-cone. Abaxial surface smooth or finely striated, often undulate, glabrous, upper margin rounded or truncate, undulate, entire or erose-denticulate, sometimes lacerate, base cuneate. Bracts broadly ovate, cuspidate, 3-6 mm long, entirely included. Seeds ovoid, 2-3 mm long, greyish brown; seed wings ovate-oblong, 10-12 × 4-5 mm, yellowish brown.
Southern Chihuahua, Nuevo León (Mexico), Arizona, Chiricahua Mts. (USA). In Mexico, this spruce is found only on the two tallest peaks of the Sierra Madre Oriental in the states of Coahuila and Nuevo León and on the tallest peak of the Sierra Madre Occidental in the state of Chihuahua, 676 km distant; 3,000-3,400 m
Red List Category & Criteria: Endangered
This subspecies has undergone an estimated recent decline (post 1950) of up to 50%. A further decline is likely so that the overall decline is estimated to be greater than 50% by 2025. This time period is within the three-generation period required by the IUCN to qualify for Endangered under the A4 criteria. In addition, the area of occupancy is much less than 100 km², there are only three known locations, subpopulations are severely fragmented and there is a continuing decline due to grazing, fire and logging.
The main population in the Sierra de la Marta (the type locality) was nearly exterminated in a forest fire in 1975. Other populations, e.g. on Cerro Mohinora in Chihuahua, are much smaller and declining, and even more susceptible to destructive fires. In addition, trees have been felled while regeneration is poor and slow due to grazing, especially on Cerro del Mohinora. Global warming presents a further threat as each subpopulation is growing close or on the summit of their respective mountains and there is little scope for further migration.
This subspecies is restricted to high altitude, N-facing slopes and ravines on limestone mountains.
This subspecies is present in one protected area (Chiricahua Mts., Arizona). Despite this that subpopulation is vulnerable to human set fires that are likely associated with illegal immigration and drug trafficing into the USA from adjoining areas of Mexico are increasingly common. The most recent fire (Horshoe 2) burnt over 200,000 ha of pine-oak and mixed conifer woodland in 2011 (US Forest Service 2011).
The Mexican subpopulations are outside formal reserves. The remaining stands of this subspecies should come under such protection, where logging, grazing and burning can be policed and controlled. Ex-situ conservation involving the collection of seed from all stands and the establishment of breeding populations in suitable areas should be a priority.
According to the Secretaría de Medio Ambiente y Recursos Naturales (Mexico) (2010) this species is in danger of extinction.
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