Exotic Herbaceous Plants

alsike clover (Trifolium hybridum)
Photo © River Valley Photographic Resources, Ltd., rvprltd.com

Alsike clover is a native of Europe. In Illinois, it may be found statewide in roadsides, fields and areas of disturbed soil. Unlike red clover (Trifolium pratense), its leaves are not marked with dark triangles. The leaves arise from branching stems. Flowers are produced from May through November. Flower color is white to pink. The species is a legume and may attain a height of one to two feet.

bird's-foot trefoil (Lotus corniculatus)

Bird’s-foot trefoil is also known as deer vetch. Found statewide, this low-growing perennial is native to Europe. It may be found in areas of moist, disturbed soil, in pastures and along roads. Flowers are produced from May through the first frost. Flowers are yellow to orange and produced in clusters. Leaves are compound and arranged alternately along the stem. The leaf has three leaflets with two leaflike stipules at the base of the leaf stalk. Each stem may be two feet in length and usually grows flat on the ground. Seeds develop in pods. The name “bird’s-foot” comes from the seed pods that fan out like a bird’s foot. The stems may form dense mats that shade out other plants. Prescribed burns on prairies can increase the spread of this species by enhancing germination of its seeds. The plant then competes with native plants. As a legume, it adds nitrogen to the soil and is eaten by birds and mammals. Bird’s-foot trefoil is widely cultivated in pastures, used for hay and used to stop erosion along roadways.

black mustard (Brassica nigra) Photo © River Valley Photographic Resources, Ltd., rvprltd.com

Black mustard is native to Europe and Asia. In Illinois, it grows statewide in areas of disturbed soil and in fields. Flowers are produced from April through October. Flowers are yellow, and each contains four petals. They are produced in clusters at the stem tip. The plant’s lower leaves are broad without deep lobes and have bristles. The upper leaves on the stem are lance-shaped and do not have bristles. The pods are held very close to the stem. Black mustard may grow from two to eight feet tall.

blackberry lily (Belamcanda chinensis)

Blackberry lily, also known as leopard flower, may grow to a height of about three feet. Its flowers are orange with purple or dark red spots. Pear-shaped seed pods develop and split open in late summer, with each pod revealing a blackberry-like seed cluster, thus the common name of "blackberry lily." This plant is native to central Asia, India, China and Japan. Sometimes used as an ornamental plant, blackberry lily may escape cultivation and spread in the wild, taking habitat from native plants.

bladder campion (Silene cucubalus)

Bladder campion, or bladder catchfly, is native to Europe and Asia. It grows in disturbed soil and along roadsides. The species is more common in the northern one-half of the state than anywhere else in the state. It may reach a height of eight to 18 inches. Flowers are produced from May through August. Each of the five, white petals per flower has a notch at the tip. A large, bulb-shaped structure supports the petals

bouncing bet (Saponaria officinalis)

Bouncing bet, or soapwort, is native to Europe. It grows in disturbed areas, roadsides and fields throughout Illinois. This perennial, herbaceous plant may attain a height of one to two and one-half feet.  Leaves are simple, opposite and joined at their base around the stem. Flowers are produced from June through September. Flowers are white or light pink and resemble phlox flowers. Each of the five petals is indented at the tip. Petals sweep back slightly from the flower’s center. Bouncing bet was originally planted as an ornamental garden species but was also used by settlers to make a type of soap. Plants can form dense patches excluding native species. All parts of the plant are toxic.

buckhorn plaintain (Plantago lanceolata)

Buckhorn plaintain is also known as English plantain. Its thin leaves have three ribs and are all located in a basal rosette. Tiny, white flowers develop in a short, fat flower head at the tip of a long, grooved stalk. This perennial plant may grow to a height of nine to 24 inches.

Buckhorn plantain may be found throughout Illinois. It grows in roadsides, lawns and field edges. Flowers are produced from April through October. Buckhorn plantain is a native of Europe that was brought to America by immigrants and has spread tremendously.

Canada thistle (Cirsium arvense)

Canada thistle, a native of Europe, is common in the northern half of Illinois and rare in the southern half. This plant is a noxious weed under Illinois law. Canada thistle may attain a height of five feet. It has deep, wide-spreading, horizontal roots. Its grooved, slender stems branch only at the top and are slightly hairy when young, becoming covered with "hair" as the plant grows. The oblong, tapering, sessile leaves are deeply divided, with prickly margins. Leaves are green on both sides with a smooth or slightly downy lower surface. Numerous small, compact, rose-purple or white flowers appear on the upper stems from June to September. Seeds are small, light brown, smooth and slightly tapered, with a tuft of tan hair loosely attached to the tip.

Canada thistle thrives in disturbed areas such as overgrazed pastures, old fields, waste places, fence rows and along roadsides. It sometimes occurs in wet areas where water levels fluctuate (along stream banks and ditches). It can invade sedge meadows and wet prairies from adjacent disturbed sites. This thistle does not do well in undisturbed prairies, good pastures or in woodlands. Plants grows in patches. Introduction to new areas occurs mostly by seed. It spreads rapidly by rhizomes (underground stems) or root segments. Lateral roots three or more feet deep spread from a fibrous taproot. Aerial shoots are sent up at two- to six-inch intervals. Basal leaves are produced the first year, flowering stems the next. Seeds remain viable in soil up to 20 years in some cases.

Canada thistle is an alien species capable of crowding out and replacing native grasses and forbs. It is detrimental to natural areas where it occurs, and it can change the natural structure and species composition where it becomes well-established.

carpet bugleweed (Ajuga reptans)

Carpet bugleweed is native to Europe. It grows in fields, roadsides and disturbed areas. In Illinois, it can be found in Cook and its surrounding counties in northeastern Illinois as well as Jackson County in southern Illinois. It is an herbaceous species that grows along the surface of the soil. Its leaves often are a shade of bronze or purple. Flowers are produced from May through July. Flowers are light blue with a short upper lip and develop in a spike. The plant attains a height of four to eight inches.

catnip (Nepeta cataria)

Catnip is a perennial herb. Its square stems identify it as a member of the mint family. The stalked, arrow-shaped leaves have toothed edges. These simple leaves are arranged opposite each other on the stem. Pale purple or white flowers with purple dots are crowded together at the stem tip. Flowers have five petals. The fruit is a nut. Catnip may grow from six to 24 inches tall. This plant's minty odor is attractive to cats. Catnip may be found throughout Illinois. It grows along railroad tracks and roads, in fields and in open woods. Flowers are produced from June through September. Catnip is a native of Europe that was transported to the United States with early settlers and has spread tremendously.

chicory (Cichorium intybus)

Chicory is a perennial herb that grows from a long taproot. Its basal leaves are similar to those of the dandelion. Stem leaves alternate and are hairy. The upper leaves clasp the stem at their base. The leaves and stem contain a milky sap. Stems are branched. Numerous one to one and one-half inch flowers are produced on the tip of the stem. The stalkless flowers are usually blue but may be white or pink. The flower rays are square-tipped and fringed. Flowers open in the morning and close each day by noon. The dry, five-sided fruit has a few scales at the tip. Chicory grows to three feet tall.

Chicory may be found throughout Illinois. It grows in open, disturbed soil and along roads. Flowers are produced from June through October. Chicory is a native of Europe that was transported to the United States with early settlers and has spread tremendously.

common dandelion (Taraxacum officinale)

The common dandelion is a perennial herb that has jagged, lobed leaves in a rosette at its base. Its hollow stem contains a milky sap. The five-parted, yellow flowers are borne in heads. The fruit is a dry, hard, winged seed. Flowers develop into fluffy, white, seed heads, each on a long stalk. Seeds may be brown or green.

The common dandelion may be found throughout Illinois. It grows in field edges, roadsides and lawns. Flowers are produced from March through November. Insects are the main agent of pollination. The common dandelion is a native of Europe and Asia that was transported to the United States with early settlers and has spread tremendously.

common forget-me-not (Myosotis scorpioides)
Photo © River Valley Photographic Resources, Ltd., rvprltd.com

Native to Europe and Asia, this species is also known as water forget-me-not or true forget-me-not. It is a perennial species that grows along streams and in areas of disturbed soil statewide. The leaves are simple and arranged alternately along the stem. Flowers are produced from April through October. Flowers are sky-blue with a yellow center on two branches that uncoil as the flowers bloom. Each flower has five petals. The plant attains a height of six inches to two feet.

common goat's-beard (Tragopogon pratensis)
Photo © River Valley Photographic Resources, Ltd., rvprltd.com

Found statewide, common goat’s-beard is native to Europe. A biennial (taking two years to complete the life cycle), this species grows in fields, roadsides and disturbed soil. Its slender, grasslike leaves clasp the stem at their base. Long bracts support the ray flowers. Flowers are produced from May through November. The flowers are yellow and close at midday. The plant may attain a height of one to three feet. The sap is white.

common periwinkle (Vinca minor)
Common periwinkle grows as a woody groundcover and is known for its glossy, evergreen leaves that are arranged oppositely on the stems. A native of Europe, periwinkle has been widely planted in gardens, homesteads and cemeteries. Although it produces light blue, star-like flowers in the early spring, it is not known to spread by seed. However, it does spread by rhizomes (underground stems). Small plantings made decades ago in some pioneer cemeteries have persisted and now completely cover the cemetery and adjacent woodlands. The waxy layer on the leaves makes them especially resistant to herbicides.

common reed (Phragmites australis)

Common reed is native to the United States in the form Phragmites australis americanus but also exists as a nonnative, invasive form, Phragmites australis australis , from Europe. This perennial grass grows in wet areas including: marshes; wetlands; roadside ditches; floodplains; shores of lakes and ponds; riverbanks; and prairies. It can be found statewide. The native subspecies does not cause problems for other native species. The European variety, though, is very invasive. A single plant may reach 15 feet tall with long leaves spreading from the stem. Flowers are produced in summer. The species spreads mainly by stolons and rhizomes but can spread by seeds, too.  It is tolerant of salinity, flooding and drought. It is not tolerant of shade. Dense clusters of the plants can form quickly, excluding many native wetland species. The hydrology of wetlands can be changed by the plants, too.

common St. John’s-wort (Hypericum perforatum)

Common St. John’s-wort is a perennial herb that grows from fibrous roots. Its stem is upright, branched and smooth. Leaves are arranged opposite each other on the stem. Each leaf is simple and oblong. The leaves have translucent spots that allow some light to pass through them. Flowers are borne in clusters. The five, yellow petals are free from each other and have black dots on their edges. The fruit is an ovoid capsule, about one-fourth inch long, which contains many seeds. Common St. John’s-wort may grow to two and one-half feet tall.

Common St. John’s-wort may be found throughout Illinois. It grows in roadsides and fields. Flowers are produced from June through September. Common St. John’s-wort is a native of Europe that was transported to the United States with early settlers and has spread tremendously.

common teasel (Dipsacus fullonum)

Common teasel is native to Europe. It was introduced to North America possibly as early as the 1700s. This species may have been introduced with other teasel species or accidentally with other plant material from Europe.

Common teasel grows as a basal rosette of leaves for a minimum of one year, then sends up a flowering stalk and dies after flowering. During the rosette stage, leaves are oval or oblong. Leaves may be "hairy" in older rosettes. Common teasel blooms from June through October. Flowering plants have large, oblong, opposite, sessile leaves that form cups (the cups may hold water) and are prickly. Stems also are prickly. Teasel's unique flower head makes the plant easy to identify when blooming. Flowers are small and packed into dense, oval-shaped heads at the tip of the flowering stems. Common teasel usually has purple flowers. Flowering stems may reach six to seven feet in height. A single teasel plant can produce more than 2,000 seeds. Teasel grows in open sunny habitats. It sometimes occurs in high quality prairies, savannas, seeps and sedge meadows, though roadsides, dumps and heavily disturbed areas are its most common habitats.

Teasel has spread rapidly in the last 20 to 30 years. This rapid range expansion probably was aided by construction of the interstate highway system. Teasel has colonized many areas along interstates. Common teasel sometimes is used as an ornamental plant, and the dried flower heads are often used in flower arrangements. Both practices have assisted its dispersal. Teasel occurs widely in Illinois. It is an aggressive exotic species that has the capacity to take over prairies and savannas if it is allowed to become established. Without any natural enemies and without any control measures, teasel can exclude all native vegetation from an area.

common yarrow (Achillea millefolium)

Common yarrow is also known as milfoil. This perennial herb has feathery, fernlike leaves which are arranged alternately along its upright stem. The lower leaves may grow to 10 inches in length. The stem may be smooth or hairy and branched or unbranched. Flowers are arranged in flat clusters at the stem tip. Two types of flowers are present. The outer flowers are white and raylike (up to six in number), while the inner flowers are yellow and tubular. Both types of flowers are fertile. The one-seeded fruit is dry and hard. Common yarrow may grow from one to three feet tall.

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

cow vetch (Vicia cracca)

Cow vetch is a native of Europe. It is found throughout Illinois. This plant may attain a height of two to three feet. The compound leaves have eight to 12 pairs of narrow, oval leaflets. The stem and leaves are "hairy." Flowers are produced from May through August. The small violet-blue flowers are clustered on one-sided spikes. Cow vetch grows in thickets, fields and roadsides. This plant may escape cultivation and spread in the wild, taking habitat from native plants.

crown vetch (Securigera varia)

Crown vetch is a low-growing, herbaceous perennial native to Europe, Asia and northern Africa. It was introduced into this country in the 1950s for erosion control purposes. The leaves are dark green and pinnately compound. The small, pink-white flowers are borne in upright clusters from June to August. Crown vetch is a prolific seeder and readily invades prairies and other open communities where it forms a dense blanket of vegetation that smothers out native plants. Crown vetch grows statewide in Illinois.

curly dock (Rumex crispus)

Curly dock is a member of the buckwheat family. This biennial or perennial herb has a taproot. Its stems are erect and unbranched. The leaves grow in a basal rosette and along the stem. Stem leaves are arranged alternately. The lance-shaped, smooth leaves are wavy along the edges and may be 10 inches long and three inches wide. Flowers are borne in whorls at the tip of the stem and in the leaf axils. The green or brown flowers are each attached to a slender, drooping stalk. The fruits have three, heart-shaped wings. Curly dock may grow to a height of four feet.

Curly dock may be found throughout Illinois. It grows in field edges, roadsides and along streams. Flowers are produced from April through May. Curly dock is a native of Europe that was transported to the United States with early settlers and has spread tremendously.

cut-leaved teasel (Dipsacus laciniatus)

Cut-leaved teasel is native to Europe. It was introduced to North America possibly as early as the 1700s. Cut-leaved teasel may have been introduced with other teasel species or accidentally with other plant material from Europe.

Cut-leaved teasel grows as a basal rosette for at least one year then sends up a flowering stalk and dies after flowering. During the rosette stage leaves are oval to oblong and may be quite "hairy." Cut-leaved teasel blooms from July through September. Flowering plants have large, oblong, opposite, sessile leaves that form cups (the cups may hold water) and are prickly. Stems also are prickly. Teasel's unique flower head makes the plant easy to identify when it is blooming. Flowers are small and packed into dense oval-shaped heads. The heads are located at the tip of the flower stems. Cut-leaved teasel usually has white flowers. Flowering stems may reach six to seven feet in height. A single teasel plant can produce more than 2,000 seeds. Teasel grows in open sunny habitats, ranging from wet to dry conditions. Cut-leaved teasel sometimes occurs in high quality prairies, savannas, seeps and sedge meadows, though roadsides, dumps and heavily disturbed areas are the most common habitats of teasel.

Teasel has spread rapidly in the last 20 to 30 years. This rapid range expansion probably was aided by construction of the interstate highway system. Teasel has colonized many areas along interstates. The use of teasel in flower arrangements has aided its dispersal, too. Teasel occurs widely in northern and central Illinois. Teasel is an aggressive exotic species that has the capacity to take over prairies and savannas if it is allowed to become established.

Deptford pink (Dianthus armeria)

Deptford pink is an annual herb that grows an elongated root. Its stems are upright (to one and one-half feet tall) and hairy. Leaves are arranged opposite each other on the stem. Each leaf is simple and needlelike. The leaf does not have teeth along the edges but is covered with hairlike structures. A leaf may grow to three inches in length. Flowers are borne in clusters at the stem tips. Flowers are bright pink with white speckles and may be one-half inch wide. The five petals are separate from each other. The fruit is an elongate, cylindrical capsule that has five teeth at the tip.

Deptford pink may be found statewide in Illinois. It grows in fields and along roadsides. Flowers are produced from May through August. Deptford pink is a native of Europe that was transported to the United States with early settlers and has spread tremendously.

garlic mustard (Alliaria petiolata)

Garlic mustard is native to Europe. It was introduced to the United States in the late 1800s and has spread north to Canada, south to Alabama and Georgia, and west to Oregon and Washington. In Illinois, it is common in the northern one-half of the state and occurs generally statewide. This species occurs most frequently in upland and floodplain forests, savannas and along roadsides. It invades shaded areas, especially disturbed sites, and open woodlands. It is capable of growing in dense shade and in areas receiving full sun. Garlic mustard dominates the ground layer in many areas. It is a severe threat to many natural areas because of its ability to grow to the exclusion of other herbaceous species.

Garlic mustard produces a garlic-type odor from all parts of the plant. A plant may grow to four feet tall. Basal leaves are kidney-shaped while stem leaves are sharply-toothed, triangular and alternate. This plant has a two-year life cycle. Seeds germinate in early spring, young plants overwinter as basal rosettes, and adults bloom from May through June the following year. Numerous small white flowers are borne at the apex of the stem, and also at some leaf axils. Plants usually produce one flowering stem but may have as many as 10 stems from a single root. Each flower is composed of four white petals that narrow abruptly at the base. Each plant dies after producing seed. Seeds disperse when the long, slender capsules burst at maturity in August. Seeds have a 20 month dormancy period and do not germinate until the second spring after ripening. Garlic mustard has a white slender taproot, with a characteristic "s" shape at the top of the root, just below the base of the stem.

gill-over-the-ground (Glechoma hederacea) Photo © River Valley Photographic Resources, Ltd.

Native to Europe and Asia, this herbaceous perennial is also known as ground ivy, creeping Charlie and creeping Jenny. It grows in moist soil, open woods, lawns, gardens and disturbed areas statewide. A member of the mint family (four-sided stems), the plant has heart-shaped leaves with scalloped margins arranged opposite each other on the stem. The lavender-colored flowers are produced from March through July on flowering stalks that can reach one foot in height. Flowers develop in the leaf axils. The leaves remain green throughout winter. The stems grow along the surface of the ground and can form a thick ground cover that discourages the growth of other species.

golden buttons (Tanacetum vulgare)

Golden buttons, also known as tansy, is native to Europe and Asia. It grows in disturbed areas, pastures, roadsides, fields and gardens statewide. This perennial species blooms July through October, producing clusters of tightly packed yellow flowers (no ray flowers, all disk flowers). Stems may be five feet tall. Leaves are pinnately compound. This species may be toxic to cattle if they consume it, but other species eat it. Golden buttons can grow in dense stands excluding other species. It was established in North America in the 1600s as a medicinal plant in settlers’ gardens. It is sold as an ornamental and often used in dried flower arrangements.

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