Douglas-fir (Lipscomb 1993), Abeto de Douglas [Spanish].
The genus was first described by Carrière with the grand Douglas-fir of North America, Pseudotsuga menziesii, as the type species (it had formerly been placed in Pinus and Abies). Some 22 species and 3 varieties have been described, but many of these were discriminated by Flous (1937) on the basis of subtle distinctions in leaf anatomy and largely have not been upheld (Farjon 1990). The existence of two or three (three, in this treatment) North American species is well established, and it is fairly clear that Japan has a single species, but the number of species on the Asian mainland has been debated, with Farjon (1990) finding a single species and Wu and Raven (1999) finding three. Since Farjon's analysis was limited by access to relatively little mainland Chinese material, I here accept Wu and Raven's interpretation, although with some reservations, not having seen the trees, or herbarium specimens. Thus this treatment presents seven species:
Evergreen trees. Bark initially smooth with transverse resin blisters, with age becoming reddish brown, thick and corky, deeply fissured into scaly ridges or flaking. Branches often pendulous, irregularly whorled; epicormic branching common on late successional trees. Short (spur) shoots absent; leaf scars transversely elliptic, slightly raised proximally but essentially flush with twig distally (see figure at left). Buds elongate, not or slightly resinous, apex acute. Leaves borne singly, persisting 6-8 years, alternate, short-stalked, linear, flat, green and grooved above, with 2 white stomatal bands each containing 5-8 lines of stomata beneath; 2 marginal resin ducts and 1 vascular bundle. Cones borne on year-old twigs. Pollen cones axillary, cylindric. Seed cones maturing first season, terminal on short branchlets, consisting of numerous spirally arranged scales, each scale 2-ovuled. Mature cones shed whole, deflexed or pendent from a 2-10 mm long peduncle, ellipsoid, ovoid, or cylindric, lacking apophysis and umbo; scales persistent, apex rounded; bracts ± exserted, apex 3-lobed with the middle lobe long and narrow. Seeds winged; cotyledons 2-12. x=12, 13 (Lipscomb 1993, Li 1975, and pers. obs.).
Canada, USA, Mexico, Japan and China.
P. menziesii is one of commonest trees in western North America, a serious weed in New Zealand, a common ornamental and agroforestry species in Europe, and easily found in most of the rest of the world's temperate terrestrial climate zones. The other species are of relatively limited occurrence and are seldom used as ornamentals.
The genus name is derived from the Greek pseudo, false, and the Japanese tsuga, hemlock (Lipscomb 1993).
Flous, F. 1937. Révision du genre Pseudotsuga. Bull. Soc. Hist. Nat. Toulouse 71: 33-164.
Little, E.L. Jr. 1952. The genus Pseudotsuga (Douglas-fir) in North America. Leafl. W. Bot. 6: 181-198.
Last Modified 2012-11-23