Trees & Shrubs of the Eloise Butler Wildflower Garden

Quaking Aspen is a native short-lived deciduous tree, generally found growing 30 to 40 feet high but can reach 100 feet with a diameter of 1 to 1-1/2 feet. It has a narrow rounded crown of thin foliage and often forms thickets. With that said, it is to be noted that the National Champion Quaking Aspen is 130 feet high and 152 inches in circumference and scores 291 points. It is located in the Coronado National Forest in Arizona. The largest in Minnesota is near Emily MN and scores 230 points. It is 96 feet high and 123 inches in circumference which is over twice the circumference of a typical tree of the species.

The bark is smooth when young, whitish to light yellow-gray or yellow-green and thin with small black rings on the surface, becoming with age a dark gray with thick furrows, especially near the base of the tree.

Twigs are slender, hairless, and shiny brown often with a waxy film. Twigs become grayish-yellow by the third year. Buds are conical, reddish brown and may have a slight resinous coating. Flowering buds are usually on small branchlets or on distal clusters.

Leaves on this species are moderately variable but in general, are alternate, simple, 1 to 3 inches long, ovate, nearly round, with an abrupt short point, rounded to slightly heart-shaped at the base with a finely saw-toothed edge which has very fine hair - the only hair on the leaf. The leaf stalk is flattened laterally at a right angle to the leaf plane, which allows the "trembling". 1 to 2 glands may be present of the leaf stalk. The surface is shiny green above and dull green under. Fall color is golden-yellow.

The leaves are variable because P. tremuloides is moderately heterophyllous, that is, it has two types of leaves - those that are formed in the winter bud for early spring growth, known as preformed or early leaves and leaves produced later in the season known as neoformed leaves. The later leaves will be different in size and number of teeth and are the last to fall from the tree in Autumn.

Flowers: Quaking Aspen is dioecious, that is male and female flowers occur on separate trees. Flowers are in dense 1 to 3 inch long brownish-gray drooping catkins. Male (staminate) flowers have a stalked basal disk with 6 to 12 stamens. Female (pistillate) individual small flowers have a basal disk, a 2-chambered ovary and the pistil has a pair of stigmata at the tip. Both flowers have a small brown bract obscuring them, whose upper edge is deeply cut. Flowers appear before the leaves and are wind pollinated.

Seed: After pollination, the female catkins elongate up to 4 inches in length and the fertilized flowers produce an elliptical light green 2-chambered tufted seed capsule. Then the capsule splits and each chamber releases 3 to 9 seeds embedded in fine white cotton-like hair which are dispersed far and wide by the wind in early summer. A single catkin can have 70 to 100 capsules. Seed maturity varies - sometimes they are ready for release as the leaf buds are breaking or sometimes just after the leaves have formed. Trees need to be about 10 to 20 years of age to produce seed but begin flowering much earlier. Seed germinates immediately.

 

Habitat: The root system of Quaking Aspen is a series of widespread laterals with descending sinker roots. The tree forms clones, occupying a few acres in our geographic area. In the western states clones have been found occupying 17 acres. This system of cloning results in this species being considered the world's largest organism. The tree is not shade tolerant and must have well drained soils which gives it a wide variety of sites where it can grow. It regenerates from seed and from root sprouting.

Names: The genus Populus is the Latin name for the Poplar. The species tremuloides means 'resembling the trembling poplar'. The author name for the plant classification - “Michx.” is for Andre Michaux (1746-1802), French botanist who made many exploring expeditions in the U.S. collecting and cataloguing many species. Two important works of his are the Histoire des chênes de l'Amérique septentrionale (1801 - Oaks of North America), and the Flora Boreali-Americana (2 vols., 1803, published posthumously and contained the description of this tree.). His son Francois, traveled with him and the father’s notes were later used for the 3-volume North American Sylva, for which Thomas Nuttall provided some supplements. The manner in which the leaf stalks are flattened causes them to flutter in the wind, giving the name of "Quaking Aspen."

Comparisons: The bark of young trees in this genus is similar but the older bark near the base of the tree differs from species to species. Quaking Aspen does not have hairy buds like P. grandidentata (Bigtooth Aspen) and does not have the long pointed very resinous buds of P. balsamifera (Balsam Poplar). Compared to P. deltoides (Cottonwood), the leaf shape and twig shape are different.