 | Pseudotsuga lindleyana (Roezl) Carrière 1868Common NamesMexican Douglas-fir. Spanish: guayamé, hayarín, pinabete (1, 2).Taxonomic notesSyn: Tsuga lindleyana Roezl 1857; Pseudotsuga macrolepis Flous 1934; Ps. guinieri Flous 1934; Ps. menziesii var. oaxacana Debreczy & Rácz 1995 (3, 4).Commonly treated as a synonym of Ps. menziesii subsp. glaucescens (=Ps. menziesii var. glauca), but fairly distinct in the sparse foliage with few abaxial stomata; the cones are largely similar. It also differs strongly in ecology, adapted to considerably warmer climates. It probably intergrades with subsp. glaucescens in an as yet undetermined area in the north of its range, possibly at the climatic boundary of the Mogollon Rim in SE Arizona (c.f. the northern boundary of many other Mexican conifer taxa here), but more likely rather further south. Research into the taxonomy of Douglas-firs of Mexico and the extreme SW USA is still at an early stage; Mexican Douglas-fir would probably be better treated as an additional subspecies within Ps. menziesii, but the relevant combination has yet to be formally published. The situation has been clouded by the naming of an excessively large number of taxa throughout the American range of the genus by Flous (5, 6) based on cone characters that proved poorly formulated, unreliable and subject to individual variation, and a subsequent highly conservative reaction against Flous' interpretation by Little (3); here, a more considered intermediate position is taken, recognising at subspecific rank (where possible) major regional variation correlated with genetic evidence (7) and ecological adaptation, in common with recent understanding of conifer taxonomy elsewhere. The very limited preliminary evidence from Mexico (7) suggests that (at least some) Douglas-fir in NE Mexico is genetically very distinct. DescriptionTrees 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). (1, 2, 4, 8, 9).RangeMexico: 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 (4). The type locality is near Pachuca, Hidalgo (3), 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 subsp. glaucescens. 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.Big TreeDouglas-fir in Mexico is rarely a large tree, with 40 m height and 1.25 m dbh the maximum cited anwhere, for (a) tree(s) near San Dimas, Durango (1); 20-30 m is height and 40-60 cm dbh is more usual.OldestDendrochronologyEthnobotanyObservationsIt may be seen scattered among pines and Abies vejari on the NE slopes of Cerro Potosí at up to 3000 m (4), and is frequent (but rarely dominant) on other moist high altitude sites throughout Northern Mexico.RemarksMexican 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 (9), a distinct character maintained in cultivated trees in Britain (10). 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 (10); 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 (2) 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 (9). Citations(1) M. Martínez. 1953. Las Pinaceas Méxicanas. México City.(2) I.M. Johnston. 1943. Plants of Coahuila, eastern Chihuahua, and adjoining Zacatecas and Durango. Journal of the Arnold Arboretum 24: 306-339. (3) E.L. Little, Jr. 1952. The genus Pseudotsuga (Douglas-fir) in North America. Leaflets Western Botany 6: 181-198. (4) Z. Debreczy & I. Rácz. 1995. New species and varieties of conifers from Mexico. Phytologia 78: 217-243. (5) F. Flous. 1934. Deux espèces nouvelles de Pseudotsuga Américains. Bull. Soc. Hist. Nat. Toulouse 66: 211-224. (6) F. Flous. 1934. Diagnoses d'espèces et variétés nouvelles de Pseudotsuga Américains. Bull. Soc. Hist. Nat. Toulouse 66: 329-346. (7) Peng Li & W.T. Adams. 1989. Rangewide patterns of allozyme variation in Douglas-fir. Canadian Journal of Forest Research 19: 149-161. (8) A. Garcia Arevalo & M. Socorro Gonzalez Elizondo. 1998. Pinaceas de Durango. Durango. (9) M.P. Frankis, field notes & herbarium collections, NE Mexico Nov 1991. (10) M.P. Frankis 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. |
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