Plants to Watch

The following plants include newly reported species and others that while known to be invasive elsewhere, have more recently been noticed to be expanding in our region. If you find these plants in the wild, outside of a planted landscape in an area that is supposed to be managed as natural habitat, it would be prudent to target them for removal.

GRASSES

Japanese Silvergrass

Bill Johnson

Miscanthus sinensis Anderss.
Grass family (Poaceae)

Japanese silvergrass, also known as Chinese silvergrass, miscanthus, and susuki (in Japan), is native to Southeast Asia where it occurs along roadsides and disturbed sites throughout much of Japan, especially at higher elevations (3,000-4,000 ft.). It is popular and frequently planted in commercial and residential landscapes. Japanese silvergrass is found in scattered locations in most of the eastern U.S. and as far west as Missouri and Louisiana, and in California and Colorado. It is a clump-forming grass with short, inconspicuous rhizomes and is adaptable to a variety of soil types including light, well-drained, nutrient-poor soils not suitable for agriculture such as roadsides, powerline rights-of-way, railroads, and steep embankments. It prefers full sun. Mature plants have slender, upright or somewhat arching leaves up to 18 in. long, with silvery midribs, sharp tips and rough margins and feathery, fan-shaped, terminal flower panicles that are silvery to pink in color and up to 2 ft. long. Flowering occurs September through October. More than fifty ornamental forms of Miscanthus sinensis are sold in the U.S. nursery trade. Most forms set little or no seed due to self-incompatibility, meaning that pollen from other forms is needed in order to produce viable seed. The species or wild type of Miscanthus likely originated from ornamental plantings. Due to the large number of forms planted, the wild type now produces a significant amount of viable seed that is wind-dispersed. It resembles ravenna-grass and other tall showy exotic ornamental grasses. Good substitutes would include eastern gamagrass (Tripsacum dactyloides), little bluestem (Schyzachirium scopyrium) and other native grasses. Removing seedheads is one way to reduce the likelihood of spread to new areas.

Ravenna-Grass

Bill Johnson

Ripidium ravennae (L.) Trinius
Grass family (Poaceae)

Ravenna-grass, or plume-grass, is native to southern Europe and was introduced for ornamental purposes. It occurs in Delaware, District of Columbia, Florida, Georgia, Maryland, and Tennessee, as well as a number of other states across the U.S., from California to Michigan. It is a tall clumping grass with a basal tuft of leaves and flowering stalks that reach heights of 8-12 ft., towering over big bluestem and other plants and making them easily visible from a distance. The base of the clump can be several feet in diameter indicating a sizeable root mass. Control is difficult to date the most effective method has been achieved come from physically removing the plants by pulling or digging out. The leaves and stems are covered with fine hairs. Flower heads are pale, feathery plumes at the tips of the tall flower stalks. It has been observed spreading from plantings along roadsides and other disturbed edge habitats as well as in fields and other open sites. Spread is by wind-blown seed. While still fairly uncommon in our area, this species shows signs of being invasive under some conditions and should be watched and controlled whenever it spreads beyond a planting. It would be wise to find a non-weedy native substitute for this grass or at least one that is not likely to become invasive. It resembles Japanese silvergrass and other tall showy ornamental grass species. A good substitute would be eastern gamagrass (Tripsacum dactyloides). Previous names for ravenna-grass include Saccharum ravennae and Erianthus ravennae.

Small Carpetgrass/Joint-Head Grass

Arthraxon hispidus (Thunb.) Makino
Grass family (Poaceae)

Small carpetgrass, or joint-head grass, is an annual grass native to temperate and tropical Asia and Australia. It was first observed in Virginia in 1930s and may have been accidentally introduced. It is reported to be invasive throughout the mid-Atlantic from Connecticut to Tennessee. It favors sunny moist habitats like floodplains, stream banks and shorelines, as well as roads and trails and thrives in sunny areas. It is invasive in scattered locations but has not been reported to be highly invasive over large areas to date. It has upright, smooth hairless stems 1-2 ft. tall are branched with many nodes which can root when they come in contact with the ground. The leaves are 1-2 in. long by about ½ in. wide, egg- to lance-shaped with a cordate (heart-shaped) base that clasps around the stem. The leaf stem and leaf margins are visibly hairy and the leaf sheath is covered with wart-like nodules. Flowers and fruits are produced September through November in terminal finger-like clusters ½-1½ in. long. It spreads by seed that can be dispersed by moving water. It may be confused with deertongue panicgrass (Dicanthelium clandestinum), a native species, which is taller and has longer leaves that lack marginal hairs. It is a plant to keep an eye on and when possible, infestations should be eradicated to prevent potential spread.

HERBACEOUS FORBS

Broadleaf Helleborine

Paula Sullivan

Epipactis helleborine (L.) Cr. Wats. & Coult.
Orchid family (Orchidaceae)

This attractive non-native orchid superficially resembles several native lilies that occur in our region, including Virginia bunchflower (Veratrum virginicum), Appalachian bunchflower (Veratrum parviflorum) and green false hellebore (Veratrum viride). Broadleaf helleborine has irregular, bilaterally symmetrical flowers with 5 petals and all the Veratrum have regular flowers with 6 petals. This is an exotic plant that is becoming increasingly invasive throughout the region, especially in dryish, gravelly soils of forest and woodland edges. It’s been documented in the eastern U.S. for a long time. It occurs throughout the Northeast in most counties from Pennsylvania to Maine, and in scattered locations in the mid-Atlantic and Great Lakes region as well as occasional locations in the central and western states. The state of Wisconsin included this plant in its control manual for ecologically invasive plants in 1997.

Giant Hogweed

USDA APHIS

Heracleum mantegazzianum Sommier & Leview
Parsley family (Apiaceae)

DO NOT TOUCH THIS PLANT. Giant hogweed is a dangerous plant and is designated as a federal noxious weed due to its toxic sap that causes skin sensitivity to UV radiation and leads to blistering and severe burns. It is native to Europe and Asia and was introduced around 1917 for use as an ornamental plant. It is also used as a spice in middle Eastern cooking. Hogweed is a towering herbaceous biennial plant growing 15-20 ft. in height with interesting foliage and massive flower heads. The large stem is hollow, about 2 in. across and usually marked with purple blotches. The leaves are deeply lobed, sharply pointed, and up to 5 ft. across. Flowering occurs in late spring to early summer. The white flowers are arranged in large umbrella-shaped heads that can be up to 2½ ft. in diameter. Hogweed has been reported in scattered locations in the Northeast, Mid-Atlantic and Pacific Northwest regions. It grows well in a variety of habitats but prefers moist, rich soils in disturbed areas such as riverbanks, ditches and railroad right-of-ways. It spreads by seed. Do not cultivate, plant, purchase, or transplant this plant. If found, notify your state Department of Agriculture of the exact location and request assistance with control.

Goutweed

Bill Johnson

Aegopodium podagraria L.
Parsley family (Apiaceae)

Goutweed is a creeping perennial herbaceous plant native to Europe and temperate portions of Asia that was introduced to North America as an ornamental. It occurs throughout most of Canada and in the U.S. from Maine to Minnesota, south to Georgia, and in Montana, Idaho, Oregon and Washington. Goutweed flourishes in moist, shaded areas of forest edges and disturbed forests and other disturbed habitats. Goutweed grows to 3 ft. tall and has alternate, compound leaves divided twice into three leaflets that are 1-3 in. long and have toothed margins and are sometimes irregularly lobed. Leaf stalks have sheathing bases. Leaves at the top of the stem are smaller and have fewer leaflets. Most leaves are basal, with the leafstalk attached to an underground stem, or rhizome. There are “wild” forms with green foliage and cultivated forms with white-margined or variegated leaves (as shown). Flowering occurs in June. Flowers are tiny and arranged in flat-topped clusters 2-4 in. across.

Italian Arum

Bill Johnson

Arum italicum P. Mill
Arum family (Arecaceae)

Italian arum is an evergreen herbaceous ornamental plant native to African, Asia and Europe that is showing signs of being invasive in natural areas. It has showy arrow-shaped fleshy leaves with white veins and can be seen in the dead of winter in the mid-Atlantic states. It has been reported to be invasive in Rock Creek Park and the U.S. National Arboretum in Washington, D.C. and in the state of Oregon. Italian arum occurs as individual plants in low level infestations of scattered individuals over a particular area. It reproduces and spreads by seed.

Marsh Dewflower

Linda Lee, Univ. of SC

Murdannia keisak (Hassk.) Hand.-Mazz.
Spiderwort family (Commelinaceae)

Marsh dewflower, Asian spiderwort, or wart-removing herb is native to eastern Asia and was first noted in 1935 in cultivated rice paddies in South Carolina. It escaped cultivation and has become established in the wild where it is invasive and spreading. It is a low growing, sprawling herbaceous plant with lance-shaped leaves and small solitary flowers with three equal sized petals that are pink to bluish in color. Flowers are borne in the upper leaf axils beginning in late summer (September). Fruits are capsules. It is known from 18 southern states north to Maryland and the District of Columbia. It prefers damp soil along the edges of freshwater tidal marshes, pond margins and slow-moving streams and can also be found inhabiting stream banks, canals, ditches, swamp forests, and other moist to wet disturbed places. Its vigorous growth enables it to out-compete native plants by forming dense mats. Seeds are dispersed by wildlife and it can spread by root fragments during flood events. Do not purchase or plant this invasive. Hand pulling may be effective if done before the plant sets seed. Chemical treatment with glyphosate (e.g. Rodeo®) labeled for wetland use may be effective if applied before seed set but it can be a challenge to control once established.

Spanish Bluebells

Dan Wihela via Flickr

Hyacinthoides hispanica (Mill.) Rothm.
Hyacinth family (Hyacinthaceae)

Spanish bluebells is a bulbous perennial native to Spain, Portugal and northwest Africa. It is a showy spring-flowering herbaceous plant with strap-shaped leaves and nodding, lavender, bell-shaped flowers on erect stalks that stand up to 18 in. high. Plants become dormant by early summer. Previously known as Scilla campanulata and Scilla hispanica. It is currently documented to occur in the wild in Delaware, Virginia and North Carolina and may be underreported. Spanish bluebells is known to naturalize and spread, a feature appreciated and used by the horticulture industry as a marketing tool. It poses a threat to native spring-blooming wildflower species already being heavily impacted by other non-native invasives like fig buttercup, garlic mustard, and nodding star-of-Bethlehem. For these reasons, it is a plant to keep an eye on and be prepared to remove if it is found invading natural habitats.

Summer Snowflake

Bill Johnson

Leucojum aestivum L.
Lily family (Liliaceae)

Summer snowflake is an herbaceous perennial plant that flowers in spring. The flowers are white, nodding and easily identified by the small green spot on the outer tip of the petals and petal-like sepals that resembles nail polish on a fingernail. It is found throughout the eastern U.S. from Maine to Illinois, south to Texas and also in California and Oregon. It has been reported to be invasive in Fairfax County, Virginia, in habitats shared by fig buttercup (Ficaria verna) and garlic mustard (Alliaria petiolata) and is likely invasive elsewhere. Snowflake could be confused with other low-growing spring-flowering lilies with white flowers such as snowdrop (Galanthus nivalis), nodding star of Bethlehem (Ornithogalum nutans), fairy lily (Zephyranthes candida) and others.

Yellow Archangel

Bill Johnson

Lamiastrum galeobdolon (L.) Her. & Pol.
Mint family (Lamiaceae)

Yellow archangel is a perennial herbaceous groundcover native to Europe. Grown as an ornamental in Europe, it has now escaped in several states in the mid-Atlantic as well as the mid-west and west coast. It has been found growing in gardens as far north as Newfoundland, Canada. It favors deeply shady, moist habitats like floodplains, stream banks and wet areas, but it can grow in rock gardens in full sun. It has not (yet) been reported to be highly invasive over large areas, rather localized in small monocultures in natural areas adjacent to gardens or where garden waste may have been deposited. Yellow archangel may have upright stems or long groundcovering vines. The opposite, variegated silver and green leaf is persistent, oval shaped, and pubescent with large teeth on the margin. Showy yellow flowers are present April through June in shade or sun on upright stems (1-2 ft.). It spreads by root fragments or numerous seed. Hand pulling control methods were not effective, as even small root fragments efficiently and vigorously resprouted. A dense newspaper/mulch blanket can work in small areas. Effective control has been obtained with triclopyr although care must be used to avoid desirable species. Small populations should be eradicated when found as area of coverage can expand rapidly in fertile soil.

SHRUBS AND SUBSHRUBS

Castor Aralia

Bill Johnson

Kalopanax septemlobus (Thunb.) Koidz
Ginseng family (Araliaceae)

Castor aralia is a showy ornamental shrub in the same family as ginseng and English ivy (pg. 105). Harvard University’s Arnold Arboretum distributed the plant to schools across the country in 1972 to celebrate its centennial. Based on recent observations it is known from at least two sites in Maryland including Piscataway National Park in Accokeek, Maryland, and Rock Creek Park in Washington, D.C. Patches are currently limited in size but because it is able to spread vegetatively and by seed; it is a plant to watch and if possible should be removed to prevent its spread.

Jetbead

John M. Randall, TNC

Rhodotypos scandens (Thunb.) Makino
Rose family (Rosaceae)

Jetbead is a multi-stemmed deciduous shrub that was introduced from Central China, Korea and Japan in 1866 for ornamental purposes. Found in at least 17 states east of the Mississippi, it has recently come to the attention of land managers who noticed it becoming invasive in natural habitats away from intentional plantings. It is very shade tolerant and can do well in forest edges and interiors. Once established, it shades out native plants in the ground layer and inhibits native tree generation. Jetbead spreads by seed and by vegetative means. It can grow to 6 ft. in height and has opposite simple leaves 2½-4 in. long with doubly serrate toothed margins and conspicuous ribbed veins with long pointed tips. It flowers in the spring, producing white four-petaled flowers about 2 in. across. Small pale to red turning black, bead-like fruits are produced soon after flowering. Jetbead invades forests, creating a thick shrub layer that displaces native shrubs, shades out understory species and restricts tree seedling establishment.

Leatherleaf Mahonia

Bill Johnson

Mahonia bealei (Fortune) Carrière
Barberry family (Berberidaceae)

Leatherleaf mahonia is native to China. It has been planted as an ornamental and is invading woodlands in the southeastern and mid-Atlantic states. It is an evergreen shrub that grows 5-10 ft. tall. The unusual leaves are pinnately compound, about 18 in. long with 9-13 paired, glossy holly-like leaflets. The leaflet margins have 2-7 teeth per side that are about ¼ in. or less in length. Leaflets are very thick and stiff. Flowering occurs in early spring. Fragrant yellow flowers emerge from the tips of the plant in attractive spike-like sprigs. The fruits are green berries that turn bluish black with a grayish bloom. Fruits hang in grapelike clusters.

Orange-Eye Butterfly-Bush

Bill Johnson

Buddleja davidii Franch.
Snapdragon family (Scrophulariaceae)

Orange-eye butterfly-bush, or summer lilac, is native to southwestern China and was introduced into North America around 1900 for ornamental purposes. It escaped from plantings and occurs in scattered locations in the Northeast, Southeast and Mid-Atlantic and in the western U.S. from southern California to northern Washington. Butterfly-bush prefers disturbed sites and riparian areas. It is a deciduous shrub with arching stems and can grow 3-15 ft. in height. The leaves are 6-10 in. long, opposite, lanced-shaped, pale gray-green, velvety and have toothed margins. It flowers summer to fall. The flowers are produced in thick, wand-like clusters from the tips of stems. Flowers are tubular, with four petals with wavy margins and can be lilac, pink or white with a deep yellow to orange center. The flowers produce lots of nectar which attracts butterflies. It spreads by seed which is dispersed mostly by wind. A related species, Lindley’s butterfly-bush (B. lindleyana) has been reported to be invasive in natural areas in Florida.

TREES

Amur Corktree

Bill Johnson

Phellodendron amurense Rupr.
Rue family (Rutaceae)

Amur corktree is native to eastern Asia including Northern China (Manchuria, Ussuri, Amur), Korea, and Japan and was introduced into the United States in 1856 for ornamental purposes. To date, it has been reported to be invasive in scattered locations in Illinois, Maryland, Massachusetts, New York, Pennsylvania and Virginia. It prefers full sun and rich soils. Once established, it can form patches that displace native plants. It spreads by seed which is produced in abundance. Amur corktree can reach 35-45 ft. at maturity. The distinctive bark is a light golden brown on younger trees and gray-brown, ridged, and furrowed on mature trees. Bark of both young and old trees is slightly spongy or corky to the touch and has a distinctive bright neon yellow layer of inner bark that can be revealed with a quick scrape of a pocket-knife. The leaves are 10-15 in. long, opposite, pinnately compound with 5-11 (up to 13) entire leaflets that are dark green, turning bright yellow in the fall. When crushed, the leaves have a distinctive citrusy smell sometimes likened to a disinfectant or skunk odor. Male and female plants are separate (dioecious) and each bears hanging panicles of yellowish-green flowers from May through June. From mid-June to mid-July, female trees produce abundant clusters of fruits (technically drupes) which are ¼-½ in. diameter. The fruits bright are green, turning black in late summer to fall, and may remain on the tree until winter. It is a plant to watch and should be controlled as necessary.

Japanese Angelica-Tree

John M. Randall, TNC

Aralia elata (Miq.) Seem
Ginseng family (Araliaceae)

Japanese angelica tree is a deciduous shrub or small tree native to China, Korea, Japan and the Russian Federation. It occurs in Ontario, Canada and throughout much of the northeastern U.S. from New Hampshire south to Maryland and west to Michigan and Illinois. It also occurs in Oregon and Washington. It can grow to 30 ft. in height. It has prickly stems and large compound leaves that are 2 or 3 times pinnate. The leaf stalks and flower stalks may have prickles. The main lateral veins of the leaflets continue all the way to the teeth at the leaflet margin. Flowering occurs late July through August and fruits mature in August and September. Flowers are small and white and emerge from tips of stems in broad umbels 1-2 ft. across that lack a central stalk. Fruits are black and about 1/10 in. across. Angelica-tree is becoming increasingly common in the mid-Atlantic and should be watched and controlled as needed.

Sawtooth Oak

Chuck Bargeron, UGA

Quercus acutissima Carruthers
Beech family (Fagaceae)

Sawtooth oak, a tree native to eastern Asia, is popular for use in street tree plantings due to its interesting foliage and fruits (acorns). It spreads by seed that is produced in large numbers and has been found in recent years to be escaping from plantings to become invasive in wild areas, displacing native plants. Because of this, land managers recommend against the use of sawtooth oak and suggest instead that landscapers use native oaks, of which there are many species to choose. One observer noted that it readily seeds into woodland edges, meadow habitats and open areas. Sawtooth oak successfully establishes in edge habitats that are not managed by mowing or other woody plant control. With regular, annual and semiannual mowing it does not seem to persist. If not mowed, however, it is fast growing, tolerant of a wide range of moisture and temperature conditions and can become a troublesome invasive. Do not plant sawtooth oaks. If small, pull seedlings or treat leaves with glyphosate. To control large trees: cut tree and grind stump; girdle, hack and squirt glyphosate; or cut and paint stump with glyphosate. Alternative plants include shagbark hickory (Carya ovata), American beech (Fagus grandifolia), red oak (Quercus rubra) and many other lovely native trees.

VINES

Chinese Yam

Jack Ranney, Univ. of TN

Dioscorea polystachya Turcz. (previously D. oppositifolia)
Yam family (Dioscoreaceae)

Chinese yam, or cinnamon vine, is an herbaceous, deciduous, perennial twining vine native to China. It is found throughout the eastern U.S. from Arkansas to Florida and as far north as Vermont with most current occurrences in the central portion of that range. It was introduced for ornamental, food, and medicinal purposes and probably escaped cultivation in the mid-1990s. It can form dense masses of vines that cover and kill native vegetation including trees within a variety of moist disturbed habitats. The leaves are halberd-shaped with a pointed tip, a concavity between leaf base and tip, long parallel veins, a long stalk, are 3-6 in. long by 3-4 in. wide and opposite to alternate (near the tips). The stems are rounded, thin and wiry. It rarely flowers. Reproduction is mainly by aerial potato-like tubers (bulbils) in leaf axils and by underground tubers. Several vines look like Chinese yam including two native species – whorled wild yam (D. quaternata) and common wild yam (D. villosa) which have heart-shaped leaves, small hairs on upper leaf surfaces, lack aerial tubers and twine right to left. Other vines that might be confused with it include native greenbrier (Smilax sp.) which lacks the aerial tubers, typically has thorns and blue to purple berries, non-native field bindweed (Convolvulus arvensis), which has alternate leaves and showy trumpet-like flowers, and morning-glory (Ipomoea sp.) which has heart-shaped, alternate leaves.