8.
Populus tremuloides
Michaux, Fl. Bor. Amer. 2: 243. 1803.
Trembling or quaking aspen, tremble, álamo temblón
Populus aurea
Tidestrom;
P.
×
polygonifolia
F. G. Bernard;
P. tremula
Linnaeus subsp.
tremuloides
(Michaux) Á. Löve & D. Löve;
P. tremuloides
var.
aurea
(Tidestrom) Daniels;
P. tremuloides
var.
magnifica
Victorin;
P. tremuloides
var.
vancouveriana
(Trelease) Sargent
Plants
to 35 m, 10 dm diam.; moderately heterophyllous.
Bark
dark gray, shallowly furrowed only basally on large trees, (greenish or yellowish white to gray and smooth otherwise).
Branchlets
reddish brown, becoming grayish yellow by third year, round, 1.2-3.5(-5) mm diam., coarse or not, glabrous.
Winter buds
reddish brown, glabrous, (shiny), slightly resinous; terminal buds (2.5-) 4-6(-9) mm, (glabrous); flowering buds separated on branchlets or clustered distally, (4.5-)6-10(-11) mm.
Leaves
: petiole distally flattened at right angle to plane of blade, (0.7-)1-6 cm, about equaling blade length; blade somewhat circular to ovate, (1-)3-7(-12) × (0.5-) 3-7(-10.5) cm, w/l = ca. 1, base shallowly cuneate to subcordate, shouldered, basilaminar glands (0 or) 1 or 2, round, margins not translucent, not ciliate, apex acuminate to acute, abaxial surface whitish green, resin stains not obvious, (slightly glaucous), glabrous, adaxial dark green, glabrous; preformed blade margins subentire to finely crenate-serrate throughout, teeth (12-)18-30(-42) on each side, sinuses 0.1-1 mm deep, (surfaces glabrous or sparsely sericeous); neoformed blade margins finely crenate-serrate throughout, teeth (20-)25-40(-50) on each side, sinuses 0.1-1.3 mm deep.
Catkins
densely (20-)50-65(-130)-flowered, (1.7-)4-7(-12.5 in fruit) cm; floral bract apex deeply cut, ciliate.
Pedicels
0.5-1.5(-2 in fruit) mm.
Flowers:
discs narrowly cup-shaped, obviously oblique, entire, 1.3-1.8(-3 in fruit) mm diam.; stamens 6-12; anthers truncate; ovary 2-carpelled; stigmas 2, filiform, basal lobes expanded, erect.
Capsules
narrowly ovoid, (2-) 2.5-4.5(-7) mm, glabrous, 2-valved.
Seeds
(3-)5-7(-9) per placenta.
2
n
= 38, 57, 76.
Flowering Mar-Jun; fruiting May-Jul. Dry to wet, open to closed woodlands and forests, edges of meadows and prairies, talus-slopes and canyon-heads, sites of human disturbance, timber cuts, mine tailings, gravel pits, quarries, roadsides; 0-3000(-4000) m; St. Pierre and Miquelon; Alta., B.C., Man., N.B., Nfld. and Labr. (Nfld.), N.W.T., N.S., Ont., P.E.I., Que., Sask., Yukon; Alaska, Ariz., Calif., Colo., Conn., Del., Idaho, Ill., Ind., Iowa, Maine, Md., Mass., Mich., Minn., Mo., Mont., Nebr., Nev., N.H., N.J., N.Mex., N.Y., N.C., N.Dak., Ohio, Oreg., Pa., R.I., S.Dak., Tex., Utah, Vt., Va., Wash., W.Va., Wis., Wyo.; Mexico (Baja California, Chihuahua, Coahuila, Nuevo León, Tamaulipas, south to Hidalgo and the state of Mexico).
Clonal aspen groves develop rapidly following fires and other disturbances and may quickly decay in their absence as infections are transmitted through the connecting root system.
Populus tremuloides
is the most widely distributed tree in North America, found throughout cold and cool-temperate regions from coast to coast and from within the Arctic Circle to the north rim of the Valley of Mexico. It ranges from sea level in the north and east to the north slopes of high mountains in the southernmost part of its range. The southerly locations, like that on Mt. Livermore in the Davis Mountains, Texas, the most southerly stand in the flora area, may be Pleistocene relicts. Groves are often occupied by single clones and show no sexual reproduction but persist and spread by root suckers. Clone formation commonly results also in striking differences in appearance and phenology of adjacent groves or blocks of trees (B. V. Barnes 1969). Some individuals display a particularly rich, yellow autumn coloration that makes them a standout among North American trees, particularly in the West, where this richness was the basis for segregation of
P. tremuloides
var.
aurea
. There do not appear to be consistent regional differences within the species that would justify recognition of subspecies or varieties (Barnes 1975). Instead, there is as much variation from clone to clone within a region as there is among regions.
Populus tremuloides
hybridizes with both the native
P. grandidentata
(
P.
×
smithii
B. Boivin) and the Eurasian
P. alba
(
P.
×
heimburgeri
B. Boivin) in southeastern Canada and the northeastern United States (B. V. Barnes 1961; T. A. Spies and Barnes 1982).
Populus
×
smithii
occurs as far west as the Niobrara River valley, Nebraska, ca. 350 km west of the nearest present populations of
P. grandidentata
. Preformed leaves are more ovate than those of
P. tremuloides
and have larger teeth.
Populus
×
heimburgeri
has transiently tomentose twigs, buds, and abaxial leaf surfaces. Contrary to some published reports (E. Lepage 1961; T. C. Brayshaw 1965b; B. Boivin 1966b; F. G. Bernard 1968),
P. tremuloides
does not hybridize naturally with
P. angustifolia
,
P. balsamifera
, or
P. deltoides
. The correct identification of such specimens is discussed under each of the purported parents.
The closely related Eurasian aspen,
Populus tremula
Linnaeus, is sometimes cultivated in North America, particularly as a columnar staminate clone ('Erecta'). Its leaves are very similar in shape to those of
P. tremuloides
and usually have slightly larger teeth. Buds are often minutely hairy. Artificial hybrids between
P. tremula
and
P. tremuloides, P. ×wettsteinii
Hämet-Ahti, are sometimes grown for plantation forestry, particularly in the Great Lakes region.
