Exotic Herbaceous Plants

​Unless otherwise noted, photos © Illinois Department of Natural Resources. No photographs included within this information may be used on the internet, publications, or any other form of media without the photographer's express permission. All rights reserved.

hedge mustard (Sisymbrium officinale) Photo © River Valley Photographic Resources, Ltd.

Native to Europe, hedge mustard grows in disturbed soil, roadsides, woodland edges, pastures and along railroad tracks. It is present statewide although it is more prevalent in northern and central Illinois than other parts of the state. An annual, hedge mustard produces flowers from May through November. These tiny flowers have four, yellow petals. Seed pods are held close to the stem. The plant can attain a height of one to three feet. 

hedge parsley (Torilis japonica)

Hedge parsley is also known as erect hedge parsley. Native to Europe and Asia, it grows in disturbed areas, forests, roadsides and fields statewide. It is an annual that attains a height of 12 to 20 inches. Leaves are pinnately compound and placed alternately along the stem. The tiny flowers are produced in clusters at the stem tip from June through August.

Japanese knotweed (Reynoutria japonica)

Japanese knotweed has the appearance of a shrub, but it is actually an herbaceous perennial plant. It is a native of Asia and Japan that can grow to 10 feet in height. Its hollow stems, enlarged at the nodes, resemble bamboo. The white flowers are borne in late summer and are very attractive to insects. However, its primary mode of reproduction is by dense rhizomes (underground stems). This plant has been widely planted as an ornamental for the small white flowers which are borne in July and August. Once established, Japanese knotweed is extremely difficult to eradicate. Currently, Japanese knotweed is present along roadsides and ditches, but it has also invaded streamside areas in parts of the state.

Johnson grass (Sorghum halepense)

Originally native to Europe, Johnson grass grows in disturbed soil, old fields, pastures, agricultural fields, forest edges and open areas statewide. It may attain a height of eight feet and has roots up to one-half inch in diameter. Its leaves are flat with a white midrib, up to two feet long and one inch wide. The leaves are folded at the base. Flowers are produced from June through October, and the purple seed heads may be up to two feet long. This perennial plant is similar in appearance to corn. It produces thousands of seeds and up to 200 feet of rhizomes annually, and these are its methods of dispersal once it is established in an area. Seeds remain viable for more than 20 years. Johnson grass excludes native species. It can be a fire hazard in times of drought because of the large amount of its biomass. Damaged or injured Johnson grass plants can produce cyanide and be deadly to animals that eat it. The wind-born pollen produced can cause allergies in some people. The species was brought to the United States as a grass for cattle to feed on. It is classified as a noxious weed in Illinois.

musk thistle (Carduus nutans)

Musk thistle, or nodding thistle, is native to Europe. It grows in disturbed areas, pastures, roadsides and railroad rights of way statewide. It is a biennial (two years to complete life cycle) forb that may grow two to seven feet tall. Its leaves are simple, alternate and very spiny. Flowers are produced from May through November. The flower heads are red-purple, composed of hundreds of individual flowers and develop at the stem tip. A single flower head may be three inches wide. The flower head usually bends downward when it is mature. Stems are spiny. This species is classified as a noxious weed in Illinois. Plants can grow very aggressively on disturbed sites. A single plant may produce about 10,000 seeds annually of which approximately 95 percent will germinate. Seeds are viable for as long as 10 years.

orange day lily (Hemerocallis fulva)

Orange day lily is native to Europe and Asia. It grows in areas of disturbed soil, along roads, on old home sites and in fields statewide. The large, orange flowers are composed of three petals and three sepals produced on stalks that are two to four feet tall. Flowers are produced from June through August. Each flower opens for one day only. The leaves are thin, arch downward and are much shorter than the flower stalks. The species spreads mainly through roots and rhizomes. These plants can form dense clumps that exclude most other plants. 

orchard grass (Dactylis glomerata)

Orchard grass is a native of Eurasia and South Africa. It was introduced to the United States as a hay and pasture grass and has escaped from cultivation. Orchard grass may attain a height of one and one-half to five feet. Flowers are produced in rounded clusters on short, stiff side branches. Flowering occurs from May through July. Plants may be found growing in roadsides, fields and waste places and commonly invade an area after it has been disturbed. It is tolerant of both shade and bright sunshine. Orchard grass may be found throughout Illinois. Seeds remain viable for two to three years or more.

ox-eye daisy (Leucanthemum vulgare) Photo © River Valley Photographic Resources, Ltd.

This perennial plant is native to Europe and Asia. It grows in disturbed soils, roadsides, pastures and fields throughout the state. Flowers are produced from May through August. The 15 to 30 white, ray flowers surround a cluster of yellow, disk flowers. Ox-eye daisy may grow from one to three feet in height. Dense stands of this species can exclude native plants from an area. It may also have root-feeding roundworms associated with its presence that can result in reduction in biodiversity. Most animals do not eat this plant, but if cows consume large quantities of this species, any milk that they produce may be distasteful. Seeds can remain viable for 20 or more years.

parsnip (Pastinaca sativa)

Parsnip is a native of Eurasia. It can survive under almost any conditions and is commonly found in roadsides, pastures and fields. This perennial plant exists as a basal rosette of leaves for at least one year. It often flowers and produces seed during its second year, although it may not flower until later years. The thick taproot of wild parsnip is long, cone-shaped and fleshy. The stem of this plant is light green, hollow and deeply-grooved. An individual parsnip plant may attain a height of five feet. Leaves are alternate, pinnately compound and branched with saw-toothed edges. Each leaf has five to 15 oval or oblong leaflets. The small, five-petaled, yellow flowers are arranged in broad, umbrellalike clusters at the top of the stems. Flowering occurs from June through September. The blossoms give rise to an oval fruit. Some people are sensitive to the plant and develop a rash if their skin contacts the leaves or sap in the presence of sunlight. A painful rash may develop that, in some people, leaves scars which persist for several months or longer. Parsnip is most irritating at the time of flowering. Care should be taken to avoid skin contact by wearing gloves, long sleeves and long pants when near this plant. In Illinois, parsnip has become a serious problem in some moist prairies. Well-established prairies are not likely to be invaded by parsnip, although it will grow in prairie edges and disturbed areas within otherwise high-quality prairies. Once established at the edges, parsnip can spread into adjacent high-quality areas. Parsnip can be found in every Illinois county.

purple loosestrife (Lythrum salicaria)

Purple loosestrife is an herbaceous perennial that may attain a height of two to seven feet. Its leaves are arranged opposite each other along the stem. Leaves are sessile. The small, purple flowers are borne at the tip of a stiff, four-sided stem. Flowers contain five or six petals. Flowering in Illinois occurs from June through August. The fruit produced is a capsule. Purple loosestrife is a native of Europe and Asia. It was introduced to the east coast of North America in the early 1800s by immigrants as an ornamental and herb, and accidentally through seeds in the ballast of ships and the wool of sheep. Transport of seeds from these plants has allowed purple loosestrife to escape into other areas. It spread into the Midwest in the 1880s and reached Illinois in the 1940s or 1950s. Purple loosestrife invades moist areas and shallow water, making conditions unfavorable for the growth of native wetland plants. The dense clusters of purple loosestrife plants form areas which are unsuitable for cover, food or nest sites for a variety of wetland species. Purple loosestrife often becomes invasive after a disturbance, such as construction or lowering the water level in a lake. Eradication of this species is difficult due to the tremendous numbers of its seeds. Each plant can produce thousands of seeds per year, and seeds may lay dormant in the soil for many years. It can also reproduce from roots and broken stems. Purple loosestrife has no native predators in North America. Attempts at slowing or stopping its spread by using herbicides, pulling and burning have been unsuccessful. A biological control is also being used.

purple rocket (Hesperis matronalis)

Purple rocket is an herbaceous perennial of the mustard family characterized by fragrant white or purple flowers that are produced in May. A native of Europe, purple rocket was introduced into gardens during the Colonial period. By the end of the nineteenth century it was so well established along roadsides and woods that many thought that it was a native wildflower. Purple rocket competes with bluebells, phlox and other native wildflowers typical of moist woods. The seeds of this plant germinate readily, enabling it to form dense stands that exclude native wildflowers. Seeds of this plant are often included in wildflower mixes that are sold commercially.

Queen Anne's lace (Daucus carota)

Queen Anne's lace is also known as wild carrot. This biennial herb grows from an elongated taproot. The stems are upright, branched and hairy. Leaves are arranged alternately along the stem. The hairy leaves are doubly compound. Flat clusters of tiny, white flowers are produced at the stem tip. The flowers give a lace-like appearance. There is usually a single, dark purple flower or flowers in the center of the cluster. The spent flower clusters turn brown and curl, taking the shape of a bird's nest. The bracts below the flower clusters are three-forked. The fruit is a dry structure that splits at maturity into two or more sections, each containing one seed. Queen Anne's lace may attain a height of two to three feet.

Queen Anne's lace may be found throughout Illinois. It grows in field edges and roadsides. Flowers are produced from May through October. Seeds may attach to the feathers of birds or the hair of mammals and can be transmitted when these animals move. The cultivated carrot is a race of this species. Queen Anne's lace is a native of Europe that was transported to the United States with early settlers and has spread tremendously.

red clover (Trifolium pratense)

Red clover is a perennial herb with leaves arranged alternately along the stems. Each leaf is divided into three, oval, finely toothed leaflets. The leaflets are hairy and often have a dark, central spot. They may also show light, white markings. The stems of this plant are spreading or erect, branched, hairy and up to two feet long. Rounded clusters of many, purple-red, tubelike flowers develop at the stem tip. Each five-petaled flower is about one-half inch long. The fruit is an oblong pod that opens by a lid. The pod contains many seeds. Red clover may attain a height of six to 16 inches tall. This plant may be found throughout Illinois growing in field edges, roadsides and cultivated fields. Flowers are produced from May through September. Red clover is a native of Europe that was transported to the United States with early settlers and has spread tremendously.

salsify (Tragopogon porrifolius)

Salsify has grasslike leaves. Its flower and seed heads are similar to those of the common dandelion but much larger. Pointed bracts stick out beyond the rays of the flower head, giving a spiky appearance. Flower heads close in the afternoon. This plant is sometimes called "vegetable oyster" because the boiled roots are said to taste like oysters. Salsify is a native of Europe which has escaped cultivation and is now found throughout Illinois.

sand goat's-beard (Tragopogon dubius) Photo © River Valley Photographic Resources, Ltd.

Sand goat's-beard, or yellow salsify, is native to Europe. It grows statewide in disturbed soil, pastures, roadsides and open forests. The grasslike leaves are arranged alternately along the stem. Leaves can be up to one foot long. Each leaf base clasps the stem. Plants in their second year or sometimes late in their first year send up a flowering stalk that may be up to three feet tall. The large, yellow flowers are produced from May through September. Flowers open only when the sun is shining and close by noon.  The name “goat’s-beard” is due to the shape of the fluff attached to the seeds. The seed head resembles that of the common dandelion although it is much larger. This species tolerates dry conditions well. 

sericea lespedeza (Lespedeza cuneata)

Sericea lespedeza is native to Asia. It can be found statewide in Illinois in sunny areas along roadsides, in fields, in pastures, in woodlands, in wetland borders and in disturbed soil. This perennial legume grows three to six feet tall. Leaves are compound with three leaflets. Lower leaves are stemmed, but the upper leaves grasp the stem. Flowers are produced from July through October. Flowers develop in groups of two or three in the upper leaf axils and are cream-yellow with purple or pink blotches. This species is resistant to drought. It grows well on steep slopes and in places where many other plant species will not grow. It has been planted extensively for wildlife habitat. Seeds are viable for more than 20 years.

spotted knapweed (Centaurea biebersteinii)

Spotted knapweed is a perennial plant that is native to Europe. It grows in areas of disturbed soil, in pastures, along railroad tracks, in prairies and in woodlands. The species is common in the northern half of Illinois and less common elsewhere in the state. Stems may reach four feet in height. Leaves are noticeably lobed, blue-gray and arranged alternately on the stem. The small, pink flowers resemble thistle flowers and are produced in summer. The “spotted” part of the common name refers to the dark spot on each bract below the flowers. A single plant can produce up to 1,000 seeds, and they can remain viable for at least eight years. Seeds can be spread by wind and water but also on mowing equipment, hay, in seeds, in gravel, on vehicles and through other modes of transportation. Chemicals produced by this plant inhibit the growth of nearby plants, resulting in a decrease in biodiversity and loss of wildlife habitat.

sulfur cinquefoil (Potentilla recta)

Sulfur cinquefoil is also known as rough-fruited cinquefoil. This perennial herb has leaves arranged alternately along the stem. Each palmately compound leaf has five to seven leaflets. Leaflets are narrow and up to three inches long. Both stems and leaves are hairy. The upright stems are branched. Pale, yellow flowers, one-half to one inch in width, develop in a cluster at the stem tip. The five petals are free from each other and notched at the tip. The fruit is dry, hard, beaked and wrinkled. Sulfur cinquefoil may attain a height of one to two feet.

Sulfur cinquefoil may be found throughout Illinois. It grows along roads and in fields. Flowers are produced from May through July. Sulfur cinquefoil is a Native of Europe that was transported to the United States and has spread tremendously.

timothy (Phleum pratense)

Timothy is a perennial plant that has leaves in an alternate arrangement along the stem. Each entire, simple leaf is linear in shape. Three-parted flowers are borne in a spike. The fruit is a grain.

Timothy may be found throughout Illinois. It grows in roadsides, fields and field edges. Flowers are produced from June through August. The pollen from this plant is a prominent cause of hay fever. Timothy is the most important dry grass and hay grass in the United States. This plant is a native of Europe that was brought to the United States with settlers and has spread tremendously.

white loosestrife (Lysimachia clethroides)

Native to Japan, white loosestrife grows in areas of disturbed soil at scattered locations throughout the state. It is often planted as an ornamental species in gardens. White loosestrife grows two to three feet tall and spreads aggressively by underground stems to form large colonies. It is a perennial plant. Flowers are produced in July and August.  Many, star-shaped, white flowers are densely packed into slender, tapered, arching clusters.

white sweet clover (Melilotus albus)

White sweet clover is a biennial or annual herb that grows from fibrous roots. The leaves are arranged alternately along the stem. Each compound leaf has three leaflets that are about one inch in length. Leaflets are toothed, lance-shaped and smooth or hairy. Stems are upright, branched and smooth. White flowers are clustered on spikes. A spike may be four inches long. The five-petaled flowers are attached to a short stalk. The fruit is a pod that is less than one-sixth inch long and slightly hairy. White sweet clover may attain a height of two to eight feet. White sweet clover may be found statewide in Illinois. It grows on bluffs, in old fields and along roads. Flowers are produced from May through October. Insects are the main agent of pollination. White sweet clover is a native of Europe and Asia. It was brought to the United States by European settlers and has spread tremendously.

winter vetch (Vicia villosa)

Winter vetch is an annual herb, producing hairy stems that spread along the ground, to a length of two feet. The leaves are arranged alternately along the stem. Each leaf is pinnately divided into 12 to 16, narrow, oblong leaflets. Flowers are produced in clusters at the stem tip. A flower cluster may be four inches long. The violet and white petals are united into a tubular shape. Each flower is about one-half inch long. The fruit is an oblong pod, about one and one-fourth inches in length.

Winter vetch may be found throughout Illinois. It grows in fields and roadsides. Flowers are produced from June through August. Winter vetch is a native of Europe that was transported to the United States with early settlers and has spread tremendously.

yellow iris (Iris pseudacorus) Photo © River Valley Photographic Resources, Ltd., rvprltd.com

Yellow iris is native to Europe, Asia and Africa. In Illinois it grows in wet, disturbed soil in marshes, ditches and other moist-soil areas statewide. This perennial species blooms from June through August producing yellow flowers at the top of stems that may be one to three feet tall. The leaves are thin and very long (up to three feet). Both leaves and flowers grow from an underground stem (rhizome). This species can tolerate water that is somewhat acidic, water that is somewhat salty, droughts and low soil oxygen. Yellow iris plants can grow in dense clusters that exclude native species. The rhizomes can trap sediments, leading to soil buildup and change in plant composition of the wetland. Most animals will not eat the leaves, but pollinators visit the flowers. This species is commonly used as a plant in water gardens and has been sold in the United States as an ornamental since the mid-1800s.

yellow sweet clover (Melilotus officinalis)

Yellow sweet clover is an annual herb. Its leaves are arranged alternately along the stem. Each leaf is divided into three leaflets. The oblong leaflets may be up to one inch long. Stems are upright, branched and smooth. Yellow, tubelike flowers are borne in thin spikes. Each flower has five petals. The fruit is a pod containing seeds. Yellow sweet clover may attain a height of two to seven feet.

Yellow sweet clover maybe found throughout Illinois. It grows at the edges of fields and along roads. Flowers are produced from June through September. Yellow sweet clover is a native of Europe that was brought to this country by early European settlers and has spread tremendously.

yellow rocket (Barbarea vulgaris) Photo © River Valley Photographic Resources, Ltd.

Native to Europe, this herbaceous plant grows in disturbed soil, roadsides, along rivers and on ditch banks. It may be found statewide. A member of the mustard family, the plant produces flowers from April to June. These small, yellow flowers have four petals each. Clasping leaves that are broad and toothed develop on the upper stem. Basal leaves have a large, rounded lobe at the tip with smaller lobes closer to the stem. The plant may reach one to two feet in height. Yellow rocket is also known as winter cress.

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