2.
Populus trichocarpa
Torrey & A. Gray, Icon. Pl. 9: plate 878. 1852.
Black cottonwood, baumier de l'ouest
Populus balsamifera
Linnaeus subsp.
trichocarpa
(Torrey & A. Gray) Brayshaw;
P. trichocarpa
var.
ingrata
(Jepson) Parish
Plants
to 75 m, 26 dm diam.; moderately heterophyllous.
Bark
grayish brown, deeply furrowed.
Branchlets
reddish brown, becoming gray by third year, round, 1.5-3(-7) mm diam., coarse, usually densely hairy.
Winter buds
red, sparsely hairy or glabrous, resinous (resin red, abundant, very fragrant); terminal buds 8-15(-20) mm; flowering buds clustered distally on branchlets, 18-20 mm.
Leaves
: petiole cylindrical or distally slightly flattened in plane of blade (often markedly swollen distally), 1-5(-9.5) cm, 1/2 blade length, (glabrous or sparsely pubescent); blade usually triangular-ovate or narrowly ovate to cordate, (3-) 5-9(-15) × (1-)2.5-6(-10) cm, w/l = 1/2-2/3, base rounded to cordate, basilaminar glands 0-2, round, margins not translucent, not ciliate, apex obtuse to acute, abaxial surface white to grayish white or greenish white with red resin stains, sparsely pubescent, adaxial dark green, glabrous; preformed blade margins very finely, evenly crenate-serrate throughout, teeth (20-)35-40 (-50) on each side, sinuses 0.1-0.4 mm deep; neoformed blade margins finely, evenly crenate-serrate throughout, teeth (25-)40-60 on each side, sinuses 0.2-0.6 mm deep.
Catkins
densely (10-)25-50(-90)-flowered, (4.5-) 7-10(-17 in fruit) cm; floral bract apex deeply cut, not ciliate.
Pedicels
0.5-2.5(-3 in fruit) mm.
Flowers:
discs broadly cup-shaped, not obviously oblique, entire, 4-6 mm diam.; stamens 30-50(-60); anthers truncate; ovary 3- or 4-carpelled, spherical, (hairy); stigmas 2-4, platelike, expanded, spreading.
Capsules
spherical, (6-) 7-9 mm, densely hairy to glabrate, 3- or 4-valved.
Seeds
(6-)10-15(-19) per placenta.
2
n
= 38.
Flowering early spring. Floodplains, lake margins, mesic areas, taluses and other slopes to subalpine tree line; 0-2600(-3000) m; Alta., B.C.; Alaska, Calif., Idaho, Mont., Nev., Oreg., Utah, Wash., Wyo.; Mexico (Baja California).
Populus trichocarpa
has been mistakenly reported from North Dakota based on specimens of
P
. ×
jackii
(
P. balsamifera
×
P. deltoides
). It hybridizes with
P. balsamifera
to form
P. ×hastata
Dode along the northern Rocky Mountain axis (Alaska, Alberta, British Columbia, and Idaho). Hybrids have capsules with 2-4 glabrous or sparsely hairy valves. The extent of hybridization has led to treatment of
P. trichocarpa
as a subspecies of
P. balsamifera
(T. C. Brayshaw 1965; L. A. Viereck and J. M. Foote 1970); these two balsam poplars are more closely related to Asian members of sect.
Tacamahaca
than they are to each other (J. E. Eckenwalder 1996). Mountain ranges of the Intermountain Region (California, Idaho, Nevada, Oregon, and Utah) have trees intermediate between
P. trichocarpa
and
P. angustifolia
. These hybrids have narrower leaves with shorter petioles and sparsely hairy capsules with 2-3 valves.
In addition to hybridizing with other North American species of sect.
Tacamahaca, Populus trichocarpa
also hybridizes with both native species of sect.
Aigeiros. Populus
×
generosa
A. Henry (synonym
P.
×
interamericana
van Broekhuizen), a hybrid between
P. trichocarpa
and
P. deltoides
, is rare in the far western area of the range for
P. deltoides
subsp.
monilifera
, where it overlaps with the more drought-tolerant inland
P. trichocarpa
(Idaho, Montana, Washington, and Wyoming) (J. E. Eckenwalder 1984). This hybrid has also been grown artificially, and such hybrids between coastal
P. trichocarpa
and
P. deltoides
subsp.
deltoides
are becoming increasingly important plantation trees in the Pacific Northwest from northern Oregon to British Columbia, as well as in Europe. They are perhaps the fastest growing of all poplars in volume, with the rapid height growth of
P. trichocarpa
added to the steady diameter growth of
P. deltoides
(R. F. Stettler et al. 1988).
Populus
×
parryi
Sargent, a hybrid between
P. trichocarpa
and
P. fremontii
, is commonly found in a wide variety of mesic habitats throughout the region of sympatry between its parents in California and Nevada (and beyond the range of
P. trichocarpa
in Mohave County, Arizona; J. E. Eckenwalder 1992). It can be found particularly in canyons where its parents are elevationally separated but overlap as permanent streams spill out into lower elevations (Eckenwalder 1984, 1984b). A morphologically and ecologically distinctive race of
P. trichocarpa
in coastal southern California with heart-shaped leaves may have arisen through this kind of hybridization (Eckenwalder 1984c). This race includes the type of
P. trichocarpa
from Ventura County.
Populus maximowiczii
A. Henry is an Asian balsam poplar that is sometimes cultivated as an ornamental, but usually as a plantation tree or parent of plantation hybrids. It is distinguished from
P. trichocarpa
and
P. balsamifera
by its elliptic leaves with rugose adaxial surfaces.
