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 North American species (one with two or more infraspecific taxa) is well established, and it is fairly clear that Japan has a single species. On the Asian mainland, with Farjon (2010) finds one species with three varieties, while Wu and Raven (1999) find three species. For the time being, I here accept Wu and Raven's interpretation, although with some reservations, not having seen the trees, or herbarium specimens. Note that Farjon would reduce P. forrestii to synonymy with P. sinensis var. sinensis (Wu and Raven distinguish the two according to the leaves; forrestii has leaves 3-5.5 cm long, and sinensis has shorter leaves), and designates a separate variety, P. sinensis Dode var. gaussenii (Flous) Silba 1990, that is not even mentioned by Wu and Raven, and which Farjon distinguishes as having reniform to broadly flabellate seed scales, much wider than long, with a truncate upper margin.
Thus this treatment presents six 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. 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, an agroforestry species and invasive 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 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).
Farjon, Aljos. 1990. Pinaceae: drawings and descriptions of the genera Abies, Cedrus, Pseudolarix, Keteleeria, Nothotsuga, Tsuga, Cathaya, Pseudotsuga, Larix and Picea. Königstein: Koeltz Scientific Books.
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 2017-12-29