Gard. Dict. Abr., ed. 4 vol. 1. 1754.
Trees evergreen, crown usually spirelike to conic, sometimes flat to round topped in age. Bark initially thin, smooth, bearing resin blisters, in age furrowed and/or flaking in plates. Branches whorled, irregular internodal branches occasionally produced by epicormic sprouting (growing from a dormant bud); short (spur) shoots absent; leaf scars prominent, ± circular to broadly elliptic, flush with twig surface, slightly depressed, or slightly raised evenly all around. Buds ovate or oblong, resinous or not, apex rounded or pointed. Leaves borne singly, persisting 5 or more years, spirally arranged but often proximally twisted so as to appear either 1-ranked (pointing up like toothbrush bristles) or 2-ranked, sessile, typically constricted and often twisted above the somewhat broadened base, sheath absent; leaves on vegetative branches flattened, frequently grooved adaxially, usually notched to rounded at apex; leaves on fertile branches sometimes appearing 4-sided, upright, sharp-pointed to rounded at apex; resin canals 2. Cones borne on year-old twigs. Pollen cones grouped, ovate or oblong-cylindric, leaving gall-like protuberances after falling, yellow to red, green, blue, or purple. Seed cones maturing in 1 season, erect, ovoid to oblong-cylindric or cylindric, not falling whole but scale by scale, cone axis persisting as an erect "spike" on branch; scales shed individually, fan-shaped, lacking apophysis and umbo; bracts included to exserted. Seeds winged, the wing-seed juncture bearing resin sac; cotyledons 4–10. x =12.
Widespread in north temperate regions, North America, Mexico, Central America, Eurasia (s to Himalayas, s China, and Taiwan), n Africa.
In Abies several traditionally accepted species have closely allied sibling species, e.g., A. balsamea -- A. fraseri, A. bifolia -- A. lasiocarpa, and A. magnifica -- A. procera. Other species may be more distinct morphologically, but many of these still appear to have evolved in geographic isolation without strong reproductive barriers developing. Thus, when distributions of species overlap, introgression between the taxa is the rule; this may make it difficult to assign certain individuals to a species. In the interests of nomenclatural stability, I have accepted the taxa recognized by the U.S. Forest Service (E.L. Little Jr. 1979). This classification does not recognize varieties based on variations in bract characteristics but recognizes species that perhaps would be treated as varieties in other conifer genera. The only exceptions to this treatment are some necessary changes within A. concolor and A. lasiocarpa. Cases of introgression are discussed under the taxa involved. Some distinct or possibly distinct geographic populations deserve further study and may warrant future taxonomic recognition.
Most North American firs are major components of vegetation, especially in the boreal, Pacific Coast coniferous, and western montane coniferous forests, where they are important for watershed management. They are cut for pulpwood and lumber and, largely from plantations, for Christmas trees. All our species, especially Abies concolor, and several exotics are grown—some more than others—as ornamentals. Firs provide cover, and their leaves are important as food, for various birds and mammals. Species of Abies frequently have a pleasant odor; their foliage has been used as a stuffing material for pillows. Most commercial products with "pine odors" are in fact scented with essential oils distilled from Abies foliage by Russian farmers. A similar oil could be derived from balsam fir in North America.
Character states used in the key are primarily those of the lowermost (i.e., the most accessible) branches.
Notes on the following features, made at the time of collection of specimens, are useful in identification.
Size and placement of resin canals in the leaves as seen in cross section with a handlens when a leaf is pulled apart or cut with a sharp knife. In Abies balsamea, A. bifolia, A. fraseri, and A. lasiocarpa the canals are ± median, placed between the abaxial epidermis and adaxial epidermis (sometimes closer to the abaxial) and in from the leaf margins; they are "large," i.e., up to about one-fourth as wide as the leaf is thick midway between the midvein and margins (each is like a tiny "eye" on each side of the midvein). In our other firs they are placed just above the abaxial margin and are "small," i.e., about one-fifth or less as wide as the leaf is thick.
Stance of the leaves, e.g., whether they are in flat sprays ("2-ranked") or point up like brush bristles ("1-ranked"), and whether some on a twig point in a direction different from others on the same twig.
Differences in color and glaucousness of the abaxial and adaxial leaf surfaces.
Shape of leaf apex as observed with a handlens.
Distribution of stomates—and number of rows of stomates—on the abaxial and adaxial leaf surfaces, particularly midway between base and apex of leaf.
Leaf-scar periderm color. Pull a leaf from a twig and note, with a handlens, the color of the scar's periphery.
Presence or absence of resin on the buds (collect a few extra buds for dissection). If buds are not available (as in the early part of the growing season), collect older branch material bearing old bud scales.
Cone color of both pollen and seed cones (binoculars are handy to note this feature of the seed cones).
Species ca. 42 (11 in the flora).
|1||Leaves stiff, apex sharply pointed; stomates absent on adaxial leaf surface; seed cones and twigs glabrous; Santa Lucia Mountains of coastal California.||Abies bracteata|
|1||Leaves flexible, apex acute, rounded, or notched; stomates usually present on adaxial leaf surface; seed cones pubescent, twigs pubescent or glabrous; widespread.||> 2|
|2||Resin canals of leaves more or less median, located well away from the epidermis.||> 3|
|2||Resin canals of leaves marginal, located near the lower epidermis.||> 6|
|3||Stomatal rows 0-4 on adaxial surface at midleaf; trans-Canadian (central Alberta to Newfoundland) and e United States.||> 4|
|3||Stomatal rows 3-6 on adaxial surface at midleaf; w North America (Alaska and sw Northwest Territories, s to California, Arizona, and New Mexico).||> 5|
|4||Stomatal rows (4-)7(-8) in each band on abaxial surface at midleaf; bracts of seed cones included or exserted; trans-Canadian and e United States (s to Iowa, Michigan, West Virginia, and n Virginia).||Abies balsamea|
|4||Stomatal rows (8-)10(-12) in each band on abaxial surface at midleaf; bracts of seed cones exserted; e montane United States (North Carolina, Tennessee, and w Virginia).||Abies fraseri|
|5||Fresh leaf scars with red periderm; basal bud scales equilaterally triangular, margins crenate or dentate; w Yukon s along coastal mountains to n California.||Abies lasiocarpa|
|5||Fresh leaf scars with tan periderm; basal bud scales isosceles triangular, margins entire; e Yukon and sw Northwest Territories s along Rocky Mountains to s Arizona and s New Mexico.||Abies bifolia|
|6||Buds not resinous, or slightly so at tips, basal scales densely pubescent; leaves mostly 1-ranked, surfaces similar in color, proximal portion curved, appressed to twig for 2-3 mm (best seen on abaxial surface of twig), distal portion of leaf divergent; California, w Nevada, w Oregon, w Washington.||> 7|
|6||Buds resinous, basal scales sparingly pubescent to glabrous (densely pubescent in Abies amabilis with leaf surfaces strikingly different in color); leaves mostly 2-ranked, surfaces similar or strikingly different in color, proximal portion more or less straight, not appressed to twig; widespread.||> 8|
|7||Basal bud scales pubescent throughout; seed cones 15-20 cm, bracts included or exserted; adaxial surface of leaves usually without longitudinal groove.||Abies magnifica|
|7||Basal bud scales pubescent centrally, glabrous at margins; seed cones 10-15 cm, bracts exserted; adaxial surface of leaves usually with longitudinal groove.||Abies procera|
|8||Stomatal rows absent on adaxial surface at midleaf; leaves strongly glaucous abaxially, green adaxially; seed cones green, blue, purple, or gray.||> 9|
|8||Stomatal rows 5-18 on adaxial surface at midleaf; leaves glaucous or green abaxially and adaxially; seed cones olive-green.||> 10|
|9||Basal bud scales densely pubescent; adaxial surface of twigs (especially in mid to upper crown) more or less concealed by forwardly directed, more or less appressed leaves, the other, usually longer leaves spreading horizontally; pollen cones at pollination red, becoming reddish yellow; mature seed cones purple.||Abies amabilis|
|9||Basal bud scales slightly pubescent or glabrous; adaxial surface of crown twigs not concealed by leaves, leaves spreading horizontally, 2-ranked, shorter and longer intermixed; pollen cones at pollination more or less blue, red, purple, orange, yellow, or green; mature seed cones light green, dark blue, deep purple, or gray.||Abies grandis|
|10||Adaxial surface at midleaf glaucous, with about (7-)12(-18) rows of stomates; leaves (2-)4-6 cm; leaf apex of lower branches usually rounded; widespread in w US but not in Sierra Nevada.||Abies concolor|
|10||Adaxial surface at midleaf not glaucous, with about (5-)7(-9) rows of stomates; leaves 2-4(-6) cm; leaf apex of lower branches weakly notched; Sierra Nevada of California and Nevada, north coastal mountains of California.||Abies lowiana|