Exotic Trees and Shrubs

Amur cork tree (Phellodendron amurense)

Amur cork tree was introduced into the United States from eastern Asia about 1874. It is frequently planted as an ornamental. This deciduous tree may grow to a height of about 35 feet and produce a wide crown. The compound leaves are dark green and composed of five to 13 leaflets. Male and female flowers occur on separate trees. Flowering occurs in June. Clusters of fleshy, black berries remain on the trees into the late fall and winter. This plant has become an invasive species because it adapts well to many different growing conditions, has no serious pests and produces large numbers of seeds.

autumn olive (Elaeagnus umbellata)

Autumn olive is native to China, Japan and Korea. It was brought to the United States in the 1830s. In the 1950s, it was promoted as a great way to control erosion while providing wildlife habitat. Many people planted it for these purposes. While it does provide some wildlife habitat, it causes more harm than good. It is a dense shrub that can grow to 20 feet tall. It grows rapidly and thickly, displacing native plants that need sunshine to grow. Each plant produces hundreds of thousands of seeds annually. It can grow in many types of habitats. Using cutting or burning to try to remove this species usually results in causing the plant to return in greater numbers than before. It can be easily spread by birds that eat the fruits and deposit the seeds in their waste materials. 

black locust (Robinia pseudoacacia)

Black locust is a deciduous tree native to the southeastern United States that can grow 60 to 80 feet in height. The pinnately compound leaves usually have two small thorns at their base. The fragrant, white, pealike flowers are borne in clusters in May and June. The fruit is a flattened pod approximately three inches long. Black locust was widely planted for its wood and attractive flowers and now grows wild throughout much of the United States. Black locust invades disturbed sites, open woods or prairie communities. It sprouts prolifically from the roots and forms dense stands that eliminate native vegetation. This ability to sprout from the roots makes it very difficult to eliminate. Black locust is native to southern Illinois and commonly planted elsewhere in the state.

glossy buckthorn (Frangula alnus)

Glossy buckthorn is a shrub native to Eurasia. It is recognized by its alternate, simple leaves, green flowers and red fruits, that turn black with age. The bark is smooth and covered with prominent lenticels, or pores, and the inner wood has a distinctive yellow color. Since being planted as an ornamental, this shrub has invaded fens, bogs and other wetlands, especially in northeastern Illinois. It has a vigorous root system, and sprouts rapidly following fires or other injuries. It produces fruit at a very early age, and mature plants produce thousands of seeds. Its control is very difficult because it is often mingled with desirable native vegetation.

Japanese barberry (Berberis thunbergii)

Japanese barberry is a native of Asia that was introduced into the United States in the late 1890s. This shrub has a rounded growth form. Its leaves are simple, alternate and spatula-shaped. There are numerous short spines on the stems. Flowers are produced from April through May. The bright red berries contain seeds that are eaten and dispersed by birds. This plant can grow in many soil types and is capable of growing in full sun or partial shade. Like other invasive exotic plants, it crowds and shades out native vegetation, especially in open woodlands. Japanese barberry grows in scattered locations throughout Illinois.

jetbead (Rhodotypos scandens)

Jetbead is a poisonous, ornamental shrub that is native to Japan. It flowers in June and July, and each flower produces a cluster of four, shiny-black, berrylike fruits that stay on the branches in winter. This shrub grows to a maximum of about six feet in height. Jetbead has green-brown twigs and smooth, doubly-serrate, opposite leaves. It occasionally escapes from cultivation and can crowd out native species.

loblolly pine (Pinus taeda)

The loblolly pine is also known as the old-field pine. This coniferous tree may grow to a height of 125 feet and a trunk diameter of two feet. It has a rounded crown. The red-brown bark is divided into plates. The leaves are needlelike, in clusters of three. Each light green needle may be nine inches long. Staminate (male) flowers are grouped in yellow spikes up to one-half inch long. Pistillate (female) flowers are in yellow clusters. The fruit is a cone, which may grow to six inches long. Each cone scale has a short, sharp prickle. The rounded seed measures about one-fourth inch long with a wing about one inch long.

The loblolly pine is a native of the southern United States but is planted statewide in Illinois. It grows in dry sites. The wood is used for pulpwood and construction. Old cones often remain on the tree.

multiflora rose (Rosa multiflora)

Multiflora rose was introduced to the eastern United States from Japan in 1886 as rootstock for cultivated roses. In the 1930s the U.S. Soil Conservation Service promoted use of multiflora rose in soil erosion control. Multiflora rose was introduced into Illinois in the 1950s for use as wildlife cover and food. Wildlife managers recognized that this thorny, bushy shrub provided excellent escape cover and a source of winter food. Because of its dense thorny nature, the commercial nursery trade began marketing it as a "living fence" as well. The species soon spread and became a serious invader of agricultural lands, pastures and natural communities throughout Illinois. Multiflora rose readily invades prairies, savannas, open woodlands and forest edges. It can form impenetrable thickets and exclude other vegetation. It is a serious pest species throughout the eastern United States. Multiflora rose is categorized as an exotic weed under the Illinois Exotic Weed Control Act of 1987. As such, the sale or planting of this species within Illinois is prohibited.

Leaves are borne alternately on the stems and divided into five to 11 leaflets. Each leaflet is oval and toothed along its margin. Clusters of numerous white flowers blossom in late spring. The fruits are small, firm, red hips that may remain on the plant into winter. The great majority of plants develop from seeds remaining in the soil relatively close to plants from which they were produced. Birds and mammals also consume the hips and can disperse them greater distances in their wastes. Rose seeds may remain viable in the soil for 10-20 years. Multiflora rose also spreads by layering, when the tips of canes touch the ground and form roots, and by plants that arise from shallow roots. Older rose shrubs may obtain a height of 15 feet or more.

Osage orange (Maclura pomifera)

Osage orange is also known as hedge apple or bow wood. This deciduous tree may attain a height of 40 feet and a trunk diameter of 12 inches. Its bark is light gray-brown with an orange tint. The bark separates into shaggy strips. Twigs are dull, orange-brown, smooth, zigzag and have short, sharp spines. The tiny buds are red-brown. Leaves are arranged alternately along the twigs. Each smooth leaf is simple, ovate and long-pointed at the tip. A single leaf may be as much as five inches long and three and one-half inches wide. Leafstalks may be two inches long. The male (staminate) and female (pistillate) flowers develop on separate trees. The small flowers are yellow-green. Male flowers are borne in clusters on stalks up to four inches long. Female flowers develop in spherical heads on short stalks. The large (up to six inches in diameter), spherical fruit is green-yellow. The fruit contains many seeds, juicy flesh and milky sap.

Osage orange may be found throughout Illinois. It grows in fence rows and wood edges. Flowers are produced from May through June. The wood of this tree is used for fence posts, archery bows, railroad ties and tool handles. The seeds are eaten by some wildlife species as a food source. Groups of these trees are often planted as windbreaks. Osage orange is a native of Arkansas, Texas and Oklahoma that has been planted in Illinois and become naturalized here.

paper mulberry (Broussonetia papyrifera)

Paper mulberry is a tree that may reach 40 feet in height. It has alternate, simple, deeply lobed leaves that are hairy underneath. A true mulberry, the red, rounded fruits develop in July and August and are eaten by birds, which disperse the seeds. A native of China, it was brought to the United States and planted as an ornamental. The trees are fast-growing and very tolerant of drought and pollution. Trees are capable of invading open areas, riparian sites and disturbed sites. Paper mulberry is found in the southern one-fourth of Illinois.

princess tree (Paulownia tomentosa)

With an annual growth in height of 15 feet, the princess tree is one of the fastest-growing trees in the world. It is a deciduous tree native to China. Its heart-shaped leaves are large and simple, and the large, fragrant flowers are borne in upright clusters. Flowers are produced from April through May. Initially planted as an ornamental, the wood is also highly prized for carving. The rounded seed pods remain on the tree throughout the winter. A single tree may produce several million seeds, which germinate readily and establish themselves in almost any type of habitat. Due to its rapid growth, it quickly outgrows native trees such as oaks or maples. Princess tree grows in the southern one-third of Illinois.

Scots pine (Pinus sylvestris)

The Scots pine is a coniferous tree that may grow to 65 feet tall and have a trunk diameter of two feet. It has an irregular crown, and its trunk is often crooked. The bark of large branches is red-brown and broken into plates. The stiff, needlelike leaves grow in clusters of two and may be three inches long. The staminate (male) flowers are in yellow spikes up to one-half inch long. The pistillate (female) flowers grow in clusters. Each cone may be about two and one-half inches long. The cone scales are smooth, without a prickle.

The Scots pine is planted statewide as an introduced species. It is a native of Europe, where it is an important lumber tree. In Illinois, it is used for Christmas trees and planted as an ornamental tree.

Siberian elm (Ulmus pumila)

Siberian elm is a fast-growing deciduous tree native to China and Siberia that has been widely planted as an ornamental. Older trees often lose their ornamental appeal due to the loss of limbs. Blooming occurs in April or early May, and the winged, flattened fruits are dispersed by wind. The small, toothed leaves are borne alternately along the stem. Tolerant of a variety of conditions, this tree rapidly colonizes open sites such as prairies. It grows throughout Illinois.

strawberry shrub (Calycanthus floridus)

Strawberry shrub is native to the southeastern United States. This deciduous shrub may attain a height of eight feet. It has opposite, simple, oval or elliptical leaves. The flowers are borne in the leaf axils, and in Illinois they appear in May and June. Each flower (one to two inches in diameter) is brown-maroon and has an odor similar to that of strawberries. The brown seeds are enclosed in an elongated, fibrous sac. This dense, bushy shrub is frequently used as an ornamental. It will grow in sun or shade. Large plants may have a width of about 12 feet. Strawberry shrub tends to form suckers, resulting in large colonies of the plants in the wild.

tree-of-heaven (Ailanthus altissima)

Tree-of-heaven is a native of China that may grow to a height of 80 to 90 feet. This deciduous species has large, pinnately compound leaves that have from 10 to 25 or more sharply pointed leaflets. The small, green flowers develop in June and are very foul-smelling. The flowers develop into flat, papery fruits that are wind-dispersed. This tree is a prolific producer of root sprouts. Though most common in disturbed habitats, such as in cities, this tree can invade streamsides and open lands such as prairies. Tree-of-heaven may be found statewide in Illinois.

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