Mexican Douglas-fir. Spanish: guayamé, hayarín, pinabete (Johnston 1943, Martínez 1953).
Syn: Tsuga lindleyana Roezl 1857; Pseudotsuga macrolepis Flous 1934; Ps. guinieri Flous 1934; Ps. menziesii var. oaxacana Debreczy et Rácz 1995 (Little 1952).
It is probably inappropriate to treat this taxon as a species distinct from Pseudotsuga menziesii. The cones, tree growth form, and principal branchlet and foliage characters all conform reasonably well to that species; yet, they are distinguishable upon close examination. The taxon is commonly treated as a synonym of Ps. menziesii var. glauca (=Ps. menziesii subsp. glaucescens), but differs in having sparse foliage with few abaxial stomata; the cones are very similar, but usually lack the reflexed bracts, and I have found them to have a somewhat larger length:width ratio. These differences are ecotypical and reflect this taxon's adaptation to a warmer and more arid climate, thus greater drought stress, than is normally the fare of glauca. Ps. lindleyana probably intergrades with var. glauca in an as yet undetermined area in the north of its range, possibly in the island ranges of southern Arizona or adjacent Sonora and Chihuahua. On balance, I feel that this species would best be described as a third variety or subspecies of Ps. menziesii, but has not yet been described as such.
There has been some prior research into this matter. Flous (1934a, 1934b) named an excessively large number of taxa throughout the American range of the genus Pseudotsuga based on cone characters that proved poorly formulated, unreliable and subject to individual variation. Little (1952) subsequently provided a categorical rejection of Flous' interpretation. It was over 30 years later that Peng and Adams (1989) presented very limited preliminary evidence from Mexico suggesting that (at least some) Douglas-fir in NE Mexico is genetically very distinct from the taxon in North America. There the situation stands, awaiting more detailed examination using a good geographic range of material to evaluate morphological and/or molecular characters using modern cladistic techniques.
Trees to 25-30 (-40) m; trunk to 60-80 (-125) cm diam, bark not very thick (compared to Ps. menziesii subsp. menziesii), smooth grey on young trees, becoming shallowly fissured, purplish-grey with yellowish-buff fissures. Crown open, thin and sparse, with level branches and slightly drooping branchlets. Leaves grey-green to drab mid-green en masse (not glaucous blue), commonly pointing forward along the shoot and slightly outcurved at the tips (particularly on vigorous shoots, more spreading on shaded shoots), short, 1-2 (-3) cm long, 1-1.2 mm wide, with two adaxial greyish stomatal bands prominent facing outward from the shoot, abaxial side facing shoot mid-green without or only with a few stomata (unlike the dense abaxial stomatal wax of at least southern populations of Ps. menziesii subsp. glaucescens); not strongly scented when bruised. Cones purple (with green bracts) ripening buff-brown, small, (2-) 3-6 (-7) cm, ovoid to ovoid-cylindric; scales not opening widely, 2-2.5 cm broad; bracts exserted 1-2 cm, moderately straight to spreading or twisted, rarely strongly reflexed (as more frequently in Ps. menziesii subsp. glaucescens). (Johnston 1943, Martínez 1953, Frankis 1991, Debreczy and Rácz 1995, Arevalo and Elizondo 1998).
Mexico: Sierra Madre Occidental, Sierra Madre Oriental, and rare in the Sierra Madre del Sur, south to Oaxaca, where two small populations were recently discovered on Peña Prieta in the San Felipe Mts just north of Oaxaca City, and on Cerro Quiexobra 110 km SE of Oaxaca City, this at 16°22'N, the southernmost locality for the whole genus (Debreczy and Rácz 1995). The type locality is near Pachuca, Hidalgo (Little 1952), about 80 km NE of Mexico City. USA: possibly in extreme SE Arizona, SW New Mexico and W Texas (Chisos Mts), but these populations are more probably Ps. menziesii var. glauca. As a matter of convenience, I treat the United States populations as P. menziesii var. glauca because U.S. authors rarely discuss the status of the species in Mexico, and the Mexican populations as Ps. lindleyana because Mexican authors usually prefer to regard Mexican Douglas-firs as taxonomically distinct from North American ones. In reality there is likely a zone of introgression or a clinal transition between the two taxa, roughly occurring in the border region or farther south, but so far research has not been done to elucidate this matter.
Usually on north-facing slopes or high valleys, at 2300-3300 m, in moist conifer or mixed forests with high summer rainfall and dry winters. USDA hardiness zone 8.
Douglas-fir in Mexico is rarely a large tree, with 40 m height and 125 cm dbh the maximum cited anwhere, for (a) tree(s) near San Dimas, Durango (Martínez 1953); 20-30 m is height and 40-60 cm dbh is more usual.
It may be seen scattered among pines and Abies vejari on the NE slopes of Cerro Potosí at up to 3000 m (Debreczy and Rácz 1995), and is frequent (but rarely dominant) on other moist high altitude sites throughout Northern Mexico.
Mexican Douglas-fir has a rather thin, sparse crown with 'dried-up' looking foliage, due to the leaves hugging the shoots closely and making the leaved shoot slender (Frankis 1991), a distinct character maintained in cultivated trees in Britain (Frankis pers. obs.). The immature cones, purple with yellow-green bracts, are very attractive and can be produced very freely on young trees only 2-3 m tall in cultivation in Britain (Frankis pers. obs.); these are the best reason for growing it as an ornamental given the fairly drab foliage.
It is surprisingly similar in foliage to some of the Abies taxa found in the same area, an interesting example of convergent evolution. Of Abies durangensis var. coahuilensis, Johnston (1943) wrote: "The Coahuilan tree grows intermixed with Pseudotsuga and simulates that tree to a truly remarkable degree. The two have not been distinguished by local people knowing the forests, and I must confess that I should not have been aware that an Abies was growing with Pseudotsuga in the Sierra Madre had I not chanced upon Abies cones cut down by squirrels". A similar convergence of foliage character exists with Abies vejari (Frankis 1991).
Arevalo, A. Garcia Arevalo and M. Socorro Gonzalez Elizondo. 1998. Pinaceas de Durango. Durango.
Debreczy, Z. and I. Rácz. 1995. New species and varieties of conifers from Mexico. Phytologia 78: 217-243.
Flous, F. 1934a. Deux espèces nouvelles de Pseudotsuga Américains. Bull. Soc. Hist. Nat. Toulouse 66: 211-224.
Flous, F. 1934b. Diagnoses d'espèces et variétés nouvelles de Pseudotsuga Américains. Bull. Soc. Hist. Nat. Toulouse 66: 329-346.
Frankis, M.P., Nov-1991 field notes & herbarium collections, NE Mexico.
Frankis, M.P., pers. obs., of trees cultivated as 'Ps. macrolepis Flous' at Bedgebury Pinetum (Kent), Bicton Park (Devon) and Wakehurst Place (Sussex), planted c. 1970 from seed from an unknown locality in Mexico.
Johnston, I.M. 1943. Plants of Coahuila, eastern Chihuahua, and adjoining Zacatecas and Durango. Journal of the Arnold Arboretum 24: 306-339.
Little, E.L., Jr. 1952. The genus Pseudotsuga (Douglas-fir) in North America. Leaflets Western Botany 6: 181-198.
Martínez, M. 1953. Las Pinaceas Méxicanas. México City.
Peng Li and W.T. Adams. 1989. Rangewide patterns of allozyme variation in Douglas-fir. Canadian Journal of Forest Research 19: 149-161.
Last Modified 2012-11-23