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A tree 80 to 100, occasionally 150 ft high, assuming as a young tree in cultivation a pyramidal form, with slightly ascending branches; young shoots pale yellowish brown, clothed with stiff, erect down. Leaves arranged all round the twig, but thinly beneath; they are 3⁄4 to 11⁄8 in. long, quadrangular, bluntish at the tips, flexible, dull, slightly glaucous-green, with three or four lines of stomata on all four surfaces. Cones 11⁄2 to 3 in. long, 3⁄4 to 1 in. in diameter; tapered towards the top, pale shining brown when mature; scales with a truncate apex and jagged margins.
Native of the mountains of western N. America from Alberta and British Columbia (where it attains its greatest size), south to New Mexico and Arizona. This handsome spruce is very hardy, and thrives better in N. Continental Europe and New England, where the winters are severe, than it does in places with a mild climate and late spring frosts. It is comparatively rare in gardens, the tree grown under the name being frequently the glaucous form of P. pungens. The two species, although so much confused, are really very distinct. P. engelmannii is easily recognised by its downy shoots; its soft and flexible, not spine-tipped leaves; also by its shorter cones.
The finest specimens of P. engelmannii grow at Dawyck in Peeblesshire; they were collected as seedlings in the Rocky Mountains by F. R. S. Balfour in 1902 and the taller of the two measures 89 × 71⁄4 ft (1974).
specimens: Dawyck, Peebl., 95 × 73⁄4 ft (1982); Kailzie, Peebl., 69 × 51⁄4 ft (1982); Fairburn, Ross, 102 × 43⁄4 ft (1982).
† P. mexicana Martinez – Allied to P. engelmannii, the Mexican spruce was discovered as late as 1961, on the border between Coahuila and Nuevo Leon, south-east of Saltillo, at about 8,000 ft. There are several stands in this area, the largest of which was almost destroyed by fire in 1975. See further the article by Keith Rushforth cited above under P. chihuahuana. There are young plants in cultivation in Britain.
This species was described by Bean (B184, S364) and Krüssmann (K191).
P. mexicana Martínez
Subsp. mexicana differs from the type subspecies in that its bark is lighter grey, its leaves are narrower (0.1–0.12 cm wide, vs. 0.15–0.2 cm in the type) and the bract scales are slightly longer (0.4–0.6 cm long, vs. 0.3–0.5 cm). Rushforth 1986, Farjon 1990, Ledig et al. 2004. Distribution MEXICO: southern Chihuahua, Coahuila, Nuevo León; USA: Arizona (Chiricahua Mts.), New Mexico (?). Gymnosperm Database 2002. Habitat North-facing mountain slopes, between 3000 and 3400 m asl. USDA Hardiness Zone 7. Conservation status Endangered. In 1975, one population (La Carmen) was decimated by a fire caused by visiting day-trippers (Rushforth 1986a). The other populations are also small and vulnerable to chance events. Cross-references S364, K196 (both as P. mexicana).
Rushforth (1987a) treats this taxon as P. mexicana Martínez, and Ledig et al. (2004) in their recent study also consider that it should be recognised as a full species, P. mexicana, though they acknowledge that it is most closely related to P. engelmannii. If political considerations are left aside, however, it seems sensible to continue to treat it as a form of the widespread P. engelmannii from north of the border and to regard it as a relict from a wider distribution, in the same way that so many other North American species have isolated pockets of occurrence in Mexico. Disjunct populations of P. engelmannii in Arizona and New Mexico are also sometimes attributed to this taxon (Farjon 1990, Taylor et al. 1994). It is rare both in the wild and in cultivation, but in southern England it seems to grow well. Two specimens at Wakehurst Place grown from Keith Rushforth’s widely distributed collection KR 526 from La Carmen, Coahuila have pendulous shoots and very glaucous leaves; the larger of the two was about 8 m tall in 2005. A 9 m specimen was measured for TROBI in 2006 by Owen Johnson at Sandling Park, Kent. Plants from J. Hjerting & S. Ødum 2 collected on Cerro Mohinora in Chihuahua are also in cultivation. Its hardiness and tolerances are not yet fully known but P. engelmannii subsp. engelmannii is renowned as an extremely hardy and adaptable tree (Sternberg 2004); the glaucous foliage of subsp. mexicana is a valuable addition to the species’ diversity in cultivation.