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Douglas fir, Carrière  1867

Pseudotsuga - Douglas fir description


Evergreen trees with a straight, single trunk bearing numerous, spirally arranged, horizontal branches not concentrated into regular tiers. Bark nonfibrous, smooth at first, flaking in scales and then quickly breaking up and finally becoming deeply furrowed between long, rectangular, blocky ridges. Crown deep, conical at first, becoming cylindrical with age. Branchlets all elongate, without distinction into long and short shoots, smooth or shallowly furrowed between the attached leaf bases, usually transiently hairy. Winter buds well developed, scaly, not conspicuously resinous. Leaves spirally arranged and radiating all around the twigs, though usually somewhat parted on the upper side. Individual leaves needlelike, flexible, flat or a little plump, usually straight, the tip notched, rounded, or pointed but not prickly, the base narrowed to a short, distinct petiole attached firmly to the twig on a low scar.

Plants monoecious.  Pollen cones single, emerging from scaly buds in the axils of a few needles of the previous year that are back from the tip of the twig. Each cone with numerous, spirally arranged pollen scales, each bearing two pollen sacs. Pollen grains very large (75-115 µm in diameter), nearly spherical, quite large, almost featureless but with a broad, low, thin-walled germination dome, differing from other Pinaceae (except Larix) in lacking either a pair of air bladders or a puffy frill. Seed cones oblong, dangling singly at the tips of short side branches, maturing in a single season, the numerous, densely spirally arranged seed scales then spreading to release the seeds. Seed scales variable within species, fan-shaped to release the seeds. Seed scales variable within species, fan-shaped to diamond-shaped or circular, the three-tipped, strap-shaped bracts attached only at the base of the scales and emerging prominently between them. Seeds two per scale, wedge-shaped, the asymmetric wing derived from the seed scale, a little larger than the seed body and cupping it on one side. Cotyledons (3-)6-9(-14). Chromosome base numbers x = 12 and 13.

Wood moderately hard and heavy, fragrant, the reddish brown heartwood contrasting with the light brown sapwood. Grain uneven, with a sharp transition between early- and latewood. Vertical resin canals small, few, and irregularly distributed, the vertical water-conducting cells (tracheids) with spiral thickening, and both horizontal tracheids and resin canals present in the rays.

Lines of stomates closely spaced and regular, confined to two stomatal bands on the lower side. Each stomate sunken beneath and largely hidden by the four (or five) surrounding subsidiary cells, which are often shared between stomates in the same and adjacent lines and which are covered with a very thick cuticle showing no trace of a Florin ring. Leaf cross section with a single resin canal on each side of the single-stranded Midvein near the outer margins of the needle just inside the lower epidermis. Photosynthetic tissue with (one or) two layers of elongate palisade cells beneath the upper epidermis and (in some species) accompanying single hypodermal layer (double along the leaf midline), the remaining photosynthetic volume filled with looser spongy mesophyll radiating around the Midvein and packed more irregularly between the palisade parenchyma and the stomatal bands.

Four species in western North America and eastern Asia. Although Pseudotsuga is a small genus, the Douglas firs have engendered a great deal of scientific interest, primarily because one species, the Douglas fir (Pseudotsuga menziesii), is the single most economically important tree species in the world. The other species are all rare or local tress with little commercial importance. In addition to its importance in forestry. Douglas fir is also the sole species of the genus in general use in horticulture. The moderate number of cultivars selected to date emphasize needle length and color (primarily ranging from green to blue) and growth habit, including dwarfs of various shapes and weeping forms.

Pseudotsuga is closely related to the larches (Larix), and these two genera share a pollination mechanism unusual in the Pinaceae, where pollen grains with two air bladders are the norm. Instead of landing on a pollination droplet and being drawn directly into the ovule with the help of the air bladders, pollen grains of Pseudotsuga and Larix germinate where they fall on the bracts of the receptive seed cones, and the pollen tubes have to grow from there into the ovules to effect fertilization. Élie-Abel Carrière (1818-1896) named Pseudotsuga (Greek and Japanese “false hemlock”) 12 years after Tsuga to emphasize the differences between these two genera, even though Pseudotsuga had pollen somewhat similar to that of hemlocks. The two genera are unrelated within Pinaceae, however, since Tsuga is an abietoid genus closely related to Pseudolarix, while Pseudotsuga is a pinoid closely related to Larix. Confusion in naming reigns! The confusion also extends to the common name. The name Douglas fir may also be seen hyphenated as Douglas-fir because these trees are not true firs (Abies). In fact, as just noted, they do not belong to the same subfamily of Pinaceae as the true firs (subfamily Abietoideae) but rather to the subfamily containing pines (Pinus), spruces (Picea), and larches (Larix), the subfamily Pinoideae. Thus an alternate common name, Oregon spruce, is slightly more accurate botanically, although these trees are not true spruces either.

Both Pseudotsuga menziesii and Pseudotsuga sinensis are quite variable across their respective ranges in western North America and China, and many varieties and even species have been proposed to accommodate this variation. However, there do not seem to be any strong breaks in the variation pattern of either species that would support recognition of additional species. Because of a lack of easily interpretable morphological features linking the species differentially, their relative relatedness is a little unclear. DNA studies seem to show that the North American species are each other’s closest relatives, as are the two Asian species, so speciation has been independent on the two continents.

Douglas fir (Pseudotsuga menziesii) itself is also unusual among Pinaceae in its chromosome base number 2x = 13 pairs rather than the 12 pairs common in the family, including all other examined species of Pseudotsuga. This unusual chromosome constitution arose by the splitting of one large, symmetrical pair of chromosomes found in the other species into two one-sided pairs, thus adding a single pair to the count without adding any new genes to the chromosomes. Douglas fir was also the tree in which the peculiar conifer trait (at least compared to most green land plants) of inheritance of chloroplasts via the pollen parent rather than the seed parent was first firmly established. This was also one of the two species (along with Monterey pine, Pinus radiata) in which another peculiarity of conifer chloroplasts was discovered, the loss of a piece of DNA (the “inverted repeat”) found in all other green land plants except many members of the pea family, which have lost it independently. This species was also one of the first conifers in which inheritance of mitochondria was studied. It proved to be via the seed parent in Douglas fir, establishing a difference between members of the Pinaceae and the Cupressaceae, in which mitochondrial inheritance, like that of chloroplasts, is via pollen.

Unlike many other conifer genera, including a number of presently highly localized genera, like Cathaya, Glyptostrobus, Keteleeria, Metasequoia, Pseudolarix, and Sequoia that occurred widely across the northern hemisphere in the Tertiary, fossils of Pseudotsuga are confined to the region now occupied by the genus. They date back to the Oligocene, about 30 million years ago. This is relatively recent for a conifer genus, and if it really arose then, this might explain the closeness of the relationship among its species.



  • Farjon, A. (2010). A Handbook of the World's Conifers. Koninklijke Brill, Leiden.
  • Eckenwalder, J.E. (2009) Conifers of the World: The Complete Reference. Timber Press, Portland.
  • IUCN Red List of Threatened Species, International Union for Conservation of Nature and Natural Resources. Cambridge, UK /Gland, Switzerland

Copyright © Aljos Farjon, James E. Eckenwalder, IUCN, Conifers Garden. All rights reserved.