502 Millbrook Avenue, Randolph, NJ 07869-3799
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Plants for Your Yard

The Randolph Township Environmental Commission would like residents to recognize the importance of using native plants when installing landscaping in their yards. Native plants support our local plant and wildlife communities, do not require pesticides or fertilizer, and need less water. When invasive plants are introduced, natural habitat quality and diversity is reduced, critical habitats for threatened or endangered species are affected, and drainage and erosion patterns are altered which threatens our high quality waterways.


Native Plants

Native plants are those that were growing here prior to European settlement. They have evolved over thousands of years to be adapted to this area and to the other living creatures around them. These species have evolved in the presence of local soils and climate conditions and have developed natural defenses to insects and disease. They require less water and tolerate drought conditions better than exotic species. These characteristics make native species easy to grow, low maintenance plants with many environmental benefits.

Finding native plants at a local nursery can be difficult, as they are not always identified. Recently, however, nurseries have begun to recognize the importance of adding locally native species to their plant inventories. When purchasing plant material for your home and garden, ask the nursery staff for recommendations for native plants.

Non-Native (Exotic) Plants

Non-native (exotic) plants are those plants that were brought to the area accidentally or purposefully. Many of the flowers and vegetables you grow in your garden are non-native, such as zinnia and cabbage. Some have spread into the wild and are considered naturalized non-natives, for example, Queen-Anne’s lace.

Invasive Exotic Plants

Invasive exotic plants are those that have escaped into the wild and are destroying the native plants and ecosystems around them. Because they do not have the same checks and balances as they did in their native lands, many of these species take over and become invasive. These exotics displace naturally occurring vegetation and in the process, upset nature’s balance and diversity. Invasive plants share the following characteristics:

  • rapid growth
  • prolific reproductive capabilities including highly successful seed dispersal and germination
  • rampant spread and colonization
  • costly to control

The next section displays a list of invasive plants in our area and methods of control.


Invasive Exotic Plants in Morris County

Click on a plant name or picture to reveal detailed information.

TREES


Norway Maple
Norway Maple
Acer platanoides
Description
Norway maple is a deciduous tree that averages 90 feet tall. The leaves have five sharply pointed lobes, similar to sugar maple leaves (Univ. of DE 1998). Norway maple can be distinguished from all native species of maples occurring in New Jersey by the milky sap present when the leaf petiole is broken off from a branch. The leaves are 4 to 7 inches long and are arranged opposite along the stem. The tree produces small greenish yellow flowers in April, and the seeds are held in wind-dispersed samaras that are 1-1/2 to 2 inches long (Univ. of DE 1998). Leaves turn yellow in late autumn (Webb 1996).
Habitat
Norway maple readily establishes on disturbed sites, such as road and railroad embankments, vacant lots, and fallow fields. It also invades and establishes in natural plant communities. It is particularly successful on alluvial soils in floodplain forests and along riverbanks (see specimen records cited). It also occurs in woodlands and forests where it invades through cleared edges or blow-downs within the interior. Tolerant of air pollution, drought and salt spray, it is commonly used as a street tree in cities and coastal communities (Nowak and Rowntree 1990).
Threats
Norway maple is an aggressive colonizer able to survive under a range of habitat conditions. The dense shade produced by the canopy decreases understory plant diversity, but does not affect establishment of its own seedlings (Wyckoff and Webb 1996).
Control
Norway maple can be controlled mechanically or with herbicides. In some situations, the use of herbicides could harm native plants. Seedlings and saplings can be hand-pulled or dug out. They will resprout if all the roots are not removed (Webb 1996).
Photo: Paul Wray, Iowa State University, Bugwood.org
Tree of Heaven
Tree of Heaven
Ailanthus altissima
Description
Tree-of-heaven is a deciduous tree that can reach 90 feet tall (Hunter 1996). The bark is gray and relatively smooth. Leaves are alternate and compound with 11 to 30 lance-shaped leaflets (Hunter 1996; Virginia NHP1998). Most leaflets have 1 to 3 coarse teeth at the base of the leaflet (Virginia NHP1998). Leaves can be distinguished from sumac (Rhus hirta) by 1 to 4 small round glands on the leaflet’s underside (Hunter 1996). When the leaves are crushed, they give off a distinctive ill scent of burnt peanut butter. Trees bloom in late spring, forming small green flowers at the ends of new shoots (Hoshovsky 1998; Hunter 1996). Flowers develop into clusters of samaras, papery winged fruits with a flattened seed in the center. The seeds are winddispersed (Virginia NHP 1998). While seedlings are highly shade intolerant, saplings appear to be more tolerant of varying light conditions (Knapp and Canham 2000). Tree-of-heaven can also reproduce asexually by sprouting from stumps or roots (Hoshovsky 1998).
Habitat
Tree-of-heaven readily establishes on disturbed sites including vacant lots, roadsides, and railroad embankments (Virginia NHP1998). It can tolerate poor soils, drought and rocky conditions (TN EPPC 1998). Early New Jersey collections largely have been made from roadsides, thickets along creeks, and old house sites (see specimens cited). It can establish in old growth forests when disturbances caused by storms or insect outbreaks create gaps in the canopy (Knapp and Canham 2000). In New Jersey, it is frequent in floodplain forests and in woods occurring on trap rock or diabase, especially on the northeastern portions of the Watchung Mountains and the Palisades.
Threats
Tree-of-heaven can disperse rapidly due to its prolific seed production. A single tree can produce 325,000 seeds in a year (Hoshovsky 1998). It can outcompete indigenous plants for underground resources with its long taproot. Trees keep native vegetation from establishing by producing a toxin that accumulates in the soil. Because of its rapid growth (Knapp and Canham 2000), it quickly and significantly alters plant community structure and disrupts the process of natural plant succession.
Control
Seedlings can be hand-pulled before the taproot becomes established (Hoshovsky 1998). Once trees are established, they are very difficult to remove. Cutting trees repeatedly over several years will stress the trees and prevent seed production. Herbicides are especially effective when applied late in the growing season because the herbicide is then taken into the root system (Virginia NHP1998; Hoshovsky 1998). Herbicides could harm nontargeted native vegetation, so careful application is necessary.
Photo: Paul Wray, Iowa State University, Bugwood.org
Black Locust
Black Locust
Robinia pseudoacacia
Description
Black locust is a fast growing deciduous tree, growing up to 80 feet tall (Sargent 1922; Converse 1998; Hunter 1996). Older trees have dark brown deeply furrowed bark, and the branches usually have stout spines. The compound leaves are alternately arranged, with 7 to 21 elliptical leaflets. The fragrant white flowers, which are blotched with yellow at the base, are borne in drooping clusters in late May and early June. Red-brown 3 to 4 inch long pods develop during the summer. The seeds are reported to be viable in the soil for a minimum of 88 years (Haynes 1956). Seedlings grow rapidly and are easily identified by the presence of long paired thorns (Wieseler 1998). Trees reproduce vegetatively through extensively spreading underground runners.
Habitat
In the southern and central Appalachian Mountains, where black locust is indigenous, trees grow singly or in small groups in forests and woodlands at altitudes up to 3,500 feet (Sargent 1922; Weakley 2000). In New Jersey, black locust is abundant in successional or disturbed habitats such as old fields, roadsides, hedge-rows, railroad and utility right-of ways, waste ground, fallow agricultural fields, and dredge spoils. It also invades and readily establishes in natural plant communities such as floodplain forests and rivershores, greensand marl ravines, grasslands, and pine and oak woods (see specimen citations; D. Snyder, personal observation).
Threats
The New Jersey Forest Service describes black locust as, “one of the most aggressive successional species in New Jersey” (Martine 1998). Black locust creates dense stands in open habitats such as old fields and grasslands, where it alters the process of natural succession and displaces indigenous plant species (Hunter 1996; D. Snyder, personal observation). In riparian habitats, especially floodplain forests, it can become dominant in the overstory. Because black locust is a nitrogen fixing plant, it may change the available soil nutrients in plant communities (Converse 1998). The seeds, leaves and bark are toxic to humans and livestock (Hunter 1996).
Control
Mowing and burning are not effective because they tend to increase suckering and root sprouting (Converse 1998). Freshly cut stumps can be painted with a systemic herbicide that will enter the root system (Converse 1998; Wieseler 1998), but herbicides leaching out of the root system could harm indigenous plants. Treated stumps should be monitored for several years (Wieseler 1998).
Photo: Paul Wray, Iowa State University, Bugwood.org

SHRUBS


Japanese Barberry
Japanese Barberry
Berberis thunbergii
Description
Japanese barberry is a woody deciduous shrub with dense spiny branches. It usually grows 2 to 3 feet high. The simple rounded leaves form rosettes along the branches in an alternate pattern. It produces solitary or small clusters of yellow flowers along the stem in spring, and the fruit ripens to a bright red oblong berry in late summer. Fruits are bird dispersed and are also eaten by small mammals (Wisconsin Dept. Natural Resources 1998). It is commonly planted as an ornamental shrub and for wildlife enhancement.
Habitat
Barberry often invades alluvial woods and open forests. It also grows along forest edges and in disturbed areas. Many collected specimens grew along creek banks and river banks (see specimens cited). It occasionally grows in saturated soil in wooded calcareous swamps (D. Snyder, personal observation).
Threats
Barberry can grow in sun or shade and in many soil types (Johnson 1996). Branches touching the ground can root, and new shoots can develop from underground roots (Wisconsin Dept. Natural Resources 1998). Barberry can grow so thick in the understory of open forests that it shades out indigenous understory plants and decreases biological diversity. This could adversely affect birds and other animals dependent on the native plants (Johnson 1996). Barberry also affects soil properties, particularly pH, which can affect plant establishment (Kourtev, et al. 1998). Severe infestations of barberry can form nearly impenetrable thorny thickets that impact the recreational value of natural lands.
Control
Mechanical removal by hoe or weed wrench is effective if most of the root system can be removed (Vermont IEPFSS1998). Regular mowing can prevent reinfestation in successional fields. Herbicide treatment can be used to treat shoots that resprout (Johnson 1996). Small patches can be pulled or dug out early in the season, before seed set (Johnson 1996).
Photo: Richard Old, XID Services, Inc., Bugwood.org
Autumn Olive
Autumn Olive
Elaeagnus umbellata
Description
Autumn olive grows as deciduous shrubs or small trees. Autumn olive has small simple alternate leaves that are oval to lance-shaped (Virginia NHP1998). The underside of the leaf is covered with silver-white scales. In early spring the plant produces small, light yellow flowers along the twigs, just after leaves have appeared. Small juicy fruits ripen to pink or red, dotted with silver-white scales, in late summer. Birds eat and disperse the fruits. Russian olive is closely related to autumn olive, and can be distinguished by its narrower lance-shaped leaves, silvery on both sides, thorny branches, and yellow, dry, mealy fruits (Virginia NHP1998). Russian olive also flowers later in the spring, well after the leaves have appeared. It commonly confused with autumn olive.
Habitat
Autumn olive has nitrogen-fixing root nodules that allow it to thrive in poor soils (Sather and Eckardt 1987; Muzika and Swearingen 1998). Typical habitats for autumn olive include disturbed areas, roadsides, pastures, fields, forest edges, and open woodlands (see specimens cited). The species invades a number of uncommon or rare plant communities including limestone and trap rock woodlands, shale bluffs, glades, limestone fens and meadows, and dune thickets. It also has been found growing in saturated soils of wooded calcareous swamps (D. Snyder, personal observation).
Threats
Autumn olive could adversely affect the nitrogen cycle of native communities on poor soils (Muzika and Swearingen 1998; Sather and Eckardt 1987). It grows rapidly, resprouts when cut, and is a strong competitor. The dense shade it produces suppresses plants that require sunlight (Virginia NHP1998). At some locations, it forms dense monocultures that alter the structure of natural plant communities and reduces plant diversity.
Control
Burning and cutting stimulate resprouting. Seedlings can be dug out when the soil is moist to ensure removal of the root system. Herbicides are effective when applied in fall (Sather and Eckardt 1987), but herbicides can also harm indigenous plants. Public and governmental education is essential to controlling the further spread of this species. As recently as 1992, autumn olive was still being recommended for “habitat improvement projects designed to attract wildlife, provide barriers, beautify existing landscapes, and reclaim disturbed sites” (Dittberner, et al., 1992) with little or no warnings on its invasive nature. The species is still widely planted in New Jersey, especially along highway corridors.
Photo: James R. Allison, Georgia Department of Natural Resources, Bugwood.org
Burning Bush
Burning Bush
Euonymus alata
Description
Winged spindletree grows as a deciduous shrub or small tree to around 12 feet tall (Ebinger 1996). It has inconspicuous yellow-green flowers in the spring. Corky ridges form along the green twigs, giving the branches a winged appearance. The leaves are opposite and are elliptical in shape with toothed margins. It is also called burning bush because its leaves turn bright red to purplish red in the fall, and the seeds are contained in red or purple fruits (Ebinger 1996). The fruits are dispersed by birds.
Habitat
Winged spindletree is frequent in rich woodlands over trap rock, shale, and limestone. It also grows in alluvial soils in flood plain forests and along stream banks.
Threats
Winged spindletree replaces native shrubs in some woodland habitats (Ebinger 1996) and alters the structure of natural plant communities. Open woodlands and flood plain forests are particularly vulnerable, but upland forests are also invaded.
Control
Plants can be cut and the stumps painted with herbicide, or foliar spray can be applied in early summer for large populations (Ebinger 1996).
Photo: James H. Miller, USDA Forest Service, Bugwood.org
Tatarian Honeysuckle
Tatarian Honeysuckle
Lonicera tatarica
Description
These honeysuckles grow as upright deciduous shrubs that range from 6 to 15 feet in height (Williams 1998). Unlike most indigenous honeysuckles, the nonindigenous bush honeysuckles have hollow stems (Williams 1998). The simple, entire, opposite leaves are oblong to ovate in shape, ranging in length from 1 to 2.5 inches (Vermont IEPFSS 1998). Lonicera morrowii has downy leaves, whereas L. tatarica has smooth hairless leaves. Pairs of tubular fragrant flowers are borne in the leaf axils along the stems in spring. Lonicera morrowii has white flowers that turn pale yellow with age. Lonicera tatarica has pink to white flowers that do not turn yellow with age. The showy fruits range in color from red to orange or yellow, and each fruit contains many seeds. The fruits are dispersed by birds (Converse 1998).
Habitat
Nonindigenous honeysuckles are frequent in disturbed areas and at the edges of forests and wetlands, but they can also be found in forested areas (Vermont IEPFSS 1998; Williams 1998). Morrow’s honeysuckle tends to be more widespread than Tartarian honeysuckle, and it occupies wetter sites (Converse 1998). In New Jersey, both species have been collected from disturbed or successional habitats such as old fields, roadsides, thickets, and fencerows, but also occur in calcareous woods and bluffs, rich rocky woods, traprock glades, floodplain forests, calcareous fens, and damp woods.
Threats
The bush honeysuckles can rapidly form a dense shrub layer that can alter light availability to understory plants and deplete soil moisture and nutrients. There may also be allelopathic effects of the fruit and vegetative parts of the honeysuckles (Converse 1998). Nonindigenous bush honeysuckles may also compete with indigenous plants for pollinators; reducing seed set of indigenous plants (Williams 1998). Additionally, the fruits of the bush honeysuckles are not high in the fats and nutrients migrating birds acquire feeding on native fruits. Fruits of Lonicera morrowii honeysuckle have been shown to change the plumage color of cedar waxwings when the birds feed primarily on the fruits (Witmer 1996).
Control
Seedlings can be pulled by hand, using care to ensure that the roots are removed. However, the disturbed soil may be easily re-invaded (Converse 1998). Repeated clipping of adult plants can be successful in shaded forest habitats (Williams 1998). Well-established older stands can be cut and the stumps treated with herbicide. Seedlings can also be treated with herbicides (Converse 1998). Herbicides can damage co-existing indigenous plants, and should be used with caution.
Photo: Patrick Breen, Oregon State University, Bugwood.org
Multiflora Rose
Multiflora Rose
Rosa multiflora
Description
Multiflora rose grows as a thorny perennial shrub with arched canes (Eckardt 1987) but can also sprawl or climb in trees 10 feet or more (Gleason and Cronquist 1991; D. Snyder, personal observation). The compound leaves are divided into 4 to 11 oval leaflets with toothed margins. The leaves are arranged alternately along the stems. Multiflora rose flowers in spring and early summer with clusters of white to pinkish-white flowers. The fruits, or rose hips, mature in fall, turning bright red. A single bush is capable of producing up to a million seeds in one season (TN EPPC 1998). The seeds are dispersed by many species of birds and by other animals. The seeds are reported to remain viable for many years, perhaps as long as 10 to 20 years (Eckardt 1987; TN EPPC 1998). Multiflora rose also reproduces vegetatively from root sprouts and from the rooting of the tips of the canes (Eckardt 1987).
Habitat
Multiflora rose occurs abundantly in disturbed or successional habitats like fields, roadsides, railroad and utility rights-of-way, old home sites, thickets, and agricultural lands. It also invades natural plant communities like floodplain forests, calcareous fens, grasslands, and forest gaps. Most early collections have come from woods, roadsides, and other disturbed areas.
Threats
Multiflora rose can produce dense, impenetrable monocultures that exclude indigenous plants and restrict the movement of some animals (Eckardt 1987). It is a strong competitor for below-ground resources, inhibiting the growth of indigenous plant species and also commercial crops in adjacent agricultural fields (Eckardt 1987). It is tolerant of some shade, and of a range of moisture conditions, enabling it to invade a variety of natural plant communities. It significantly alters natural plant community structures and reduces overall biological diversity.
Control
Repeated mowing or cutting can be used to control the spread of small populations, but will not eradicate them (Eckardt 1987) since multiflora rose can resprout from stumps. Small plants can be dug out, provided the entire root is removed (Virginia NHP 1998). Plant growth regulators have been used effectively to prevent plantings from spreading, and herbicides can be used to kill plants (Eckardt 1987). Herbicides should be used with caution, as they could harm indigenous plants. Several potential biological control agents are under investigation (Eckardt 1987).
Photo: James H. Miller, USDA Forest Service, Bugwood.org
Wineberry
Wineberry
Rubus phoenicolasius
Description
Wineberry grows from biennial arching canes, which reach up to 2 m long. The leaves are divided into three leaflets whose undersides are covered in small, dense white hairs. The stems and buds are covered by dense 3 to 5 mm long purple hairs, which give the stems a shaggy appearance (Gleason and Cronquist 1991). The five-petaled flowers are white and bloom in late spring to early summer. The fruits mature in mid to late summer (Hough 1983). Fruits are red, juicy berries dispersed by birds and other animals.
Habitat
Wineberry is frequent in open or disturbed habitats such as thickets, fields, and forest edges, railroad and utility rights-of-way, and old homesites. It also successfully invades wooded ravines, floodplain forests, calcareous forests, shale bluffs, and traprock and diabase forests.
Threats
Wineberry forms an extensive, nearly impenetrable understory layer in favorable locations such as moist soils in forests over dolomite, marble, shale, diabase, and traprock (D. Snyder, personal observation). These substrates are known to support several rare plant communities and unique plant assemblages. Thickets of wineberry alter the structure of natural plant communities, outcompete rare or declining plant species, and contribute to the loss of biological diversity. In the Piedmont and the Kittatinny limestone valley of the Ridge and Valley Province, wineberry frequently occurs with the invasive nonindigenous species Japanese barberry (Berberis thunburgii), Japanese honeysuckle (Lonicera japonica), and Japanese stiltgrass (Microstegium vimineum) (D. Snyder, personal observation). Such wholly unnatural plant associations can dominate an acre or more of woodland, with an obvious reduction in the diversity of indigenous understory and herbaceous species. Bailey (1932) reported that wineberry, in association with Japanese honeysuckle and the nonindigenous invasive tree-of-heaven, had completely altered the habitat at the type locality of a rare indigenous species of blackberry in Monmouth County, New Jersey, and was directly contributing to the species decline.
Control
There is currently no control information specific to wineberry, but other Rubus species are controlled mechanically and with herbicides (Hoshovsky 1998). Small plants can be handpulled, and larger plants can be dug out. It is important to remove the root crown, as plants will resprout from the crown. Root crowns and stumps can also be treated with herbicides if left in the ground, but herbicides can harm adjacent indigenous plants.
Photo: Britt Slattery, U.S. Fish and Wildlife Service, Bugwood.org

VINES


Porcelainberry
Porcelain Berry
Ampelopsis brevipedunculata
Description
Porcelain berry is a deciduous climbing vine in the grape family. It can climb to a height of 16 feet with support. The leaves are often deeply lobed, with 3 to 5 lobes per leaf, and are slightly hairy on the underside (Virginia NHP1998). Young twigs are also hairy. Small, inconspicuous, yellow flowers bloom in mid-summer (Antenen 1996). Fruits form in late summer, and mature in the fall. The fruits are hard and change color from white to pastel shades of yellow, lilac, and green, and finally to a sky blue color (Virginia NHP1998). Seeds are primarily bird dispersed, but the plant also can reproduce vegetatively from stem or root segments (Antenen 1996).
Habitat
Porcelain berry is tolerant of a wide range of environmental conditions (Virginia NHP1998). It is frequently found in old fields and along roadsides, railroads, and powerline right-of-ways. It tends to initially colonize disturbed open areas, such as forest edges, forest gaps, shorelines, and river banks. It is especially abundant in open thickets and sand dunes along coastal portions of New Jersey (D. Snyder, personal observation).
Threats
Porcelain berry forms thick mats, blanketing the ground and trees and shrubs on forest edges. It reduces the ability of indigenous plant species to establish, and makes the trees that it covers more vulnerable to wind (Antenen 1996) and ice damage.
Control
Porcelain berry is very difficult to remove once it has become established. Small plants can be hand-pulled, preferably before the plant is in fruit to avoid scattering seeds (Virginia NHP1998). Repeated cutting or mowing will control vines, but not kill them (Antenen 1996). Plants can be shaded out gradually by planting trees or cutting vines off existing trees until they mature. Herbicide application can be effective when applied in early autumn, but may damage surrounding native plants. Treated sites need to be monitored for several years to remove new sprouts.
Photo: Jil M. Swearingen, USDI National Park Service, Bugwood.org

ANNUAL, BIENNIALS AND PERENNIALS


Garlic Mustard
Garlic Mustard
Alliaria petiolata
Description
Garlic mustard is a herbaceous biennial that ranges in height from 0.05 to 1.5 meters (Nuzzo 2000). Seedlings emerge in spring and form rosettes of kidney-shaped leaves by midsummer. During the second year of growth, plants form one or more stems with alternate, sharply-toothed, triangular to heart-shaped leaves. The plants smell like garlic when crushed, especially the young leaves. A cluster of white, four-petaled flowers form at the end of the stems and branches in spring. Garlic mustard is pollinated by a number of small bees and flies but can self-pollinate in the absence of insects (Cruden, et al.1996). The small oblong black seeds are held in siliques (long narrow capsules) at the ends of the stems (Nuzzo 2000). The seeds begin to mature in May and can remain viable through the summer (Rowe and Swearingen 1998). Garlic mustard has the ability to form seed banks but as demonstrated by Baskin and Baskin (1992), these seed reserves are viable for only about four years. People readily disperse the seeds when they get stuck on their boots or clothing and by automobiles and mowers. Seeds may also be dispersed by floodwaters, or indirectly by rodents, birds, and deer (Nuzzo 2000).
Habitat
Garlic mustard is primarily a woodland herb which grows in rich moist forests, floodplains, and along trails and forest edges (see specimens cited). It is especially abundant in soils occurring over limestone, trap rock, or diabase (D. Snyder, personal observation). It frequently establishes on disturbed areas such as a treefalls or trail edges, and then spreads into undisturbed habitats (Nuzzo 2000).
Threats
Alliaria petiolata can dominate forested understories, resulting in a decline in indigenous herb diversity (Nuzzo 2000). In turn, the decline of indigenous species alters habitat suitability for birds and other animals. Spring flowering plants and the animals dependent on them are particularly affected (Rowe and Swearingen 1998). Garlic mustard may have allelopathic effects as well, preventing plants from growing near it (Nuzzo 2000).
Control
Alliaria petiolata spreads rapidly once established. Baskin and Baskin (1992) reported that if small populations are not eradicated promptly, within a few generations, a few plants can rapidly spread and form dense populations throughout the forest. It is essential, therefore, to begin removal as soon as plants are first observed. Hand-pulling plants can control small infestations. This is most easily done when plants are small and the soil is moist (Rowe and Swearingen 1998). Plants should be pulled before seeds have matured, to prevent inadvertent dispersal. Hand-pulling should continue for at least five consecutive years in order to exhaust the seed bank. However, as Baskin and Baskin (1992) observe, it is likely that seeds will be brought in from other contaminated sites and control methods may be required indefinitely. Flower stalks can be cut in small populations to prevent seeds from maturing, and fire or herbicides can be used to control larger populations (Nuzzo 2000). Late fall is the preferred season for fire or herbicide control, because most indigenous plant species are dormant. Fire is only effective if there is a critical increase in rootcrown temperature. Rootcrowns covered by 1 to 2 cm of leaf litter will be protected. Removal of the leaf litter will increase seedling survival after the fire, necessitating a second burn the following year. Regardless of the control method used, sites must be monitored for at least five years to ensure that the seed bank has been exhausted (Rowe and Swearingen 1998).
Photo: David Cappaert, Michigan State University, Bugwood.org
Spotted Knapweed
Spotted Knapweed
Centaurea biebersteinii
Description
Spotted knapweed is a biennial to short-lived perennial herb that forms between 1 to 20 stems from a basal rosette (Mauer, et al. 1987). Seedling rosette leaves are pinnately to bipinnately dissected and grow 4 to 8 inches long. The stems can grow 1 to 3 feet tall, and lower stem leaves are pinnate, becoming linear on the upper stem (Mauer, et al. 1987). In summer, pink to white tubular flowers bloom, held in a thistle-like inflorescence at the ends of branches (Virginia NHP1998). Seeds are released from late summer through fall. Seeds disperse short distances passively, but long-distance dispersal can occur via rodents, livestock, vehicles, or commercial seed (Mauer, et al. 1987).
Habitat
Spotted knapweed primarily establishes in disturbed areas, but can spread into undisturbed areas once established (Mauer, et al. 1987). Western states are heavily invaded in overgrazed areas. It can grow under very dry, low nutrient conditions, and is often found on gravelly or sandy openings in old fields and roadsides (Virginia NHP1998). In New Jersey spotted knapweed occurs abundantly in dry to moist soils along roads, powerline right-of-ways, railroad embankments, old fields, and vacant lots. It also successfully invades many natural plant communities including sand plains, trap rock and limestone glades, shale bluffs, and limestone fens (D. Snyder, personal observation).
Threats
Spotted knapweed is an excellent competitor, and is resistant to herbivores (Mauer, et al. 1987). It has been documented that spotted knapweed outcompetes and replaces indigenous plant species (Harris and Cranston 1979). High concentrations of leachates of spotted knapweed have been reported to inhibit the germination of grass and conifer seedlings (Kelsey and Bedunah 1989). Lesica and Shelly (1996) have shown that spotted knapweed reduces recruitment and population growth of Arabis fecunda Rollins, a threatened plant species endemic to southwestern Montana. Spotted knapweed can increase erosion by displacing native root systems with its taproot (Mauer, et al. 1987). The Nature Conservancy’s Wildland Invasive Species Program (1997) is investigating a report that spotted knapweed may contain a carcinogen that causes tumors in humans. In New Jersey, spotted knapweed invades rare natural plant communities where it replaces native plant species and significantly alters plant community structure.
Control
Most control methods have been developed for large infestations of knapweed in the western United States. It may be possible to plant indigenous grasses or other species that could outcompete spotted knapweed, but most tests of this technique have been done in western states (Mauer, et al. 1987). Removing flowering heads after plants have bolted can reduce resprouting and seed dispersal. Hand-pulling or grubbing can be used to control small populations (Virginia NHP1998). Because of the knapweed’s reported, but as yet unverified, carcinogen contained in the sap, appropriate gloves should be worn when handling this species. Herbicides can be used, but they do not prevent germination from the seed bank. Four biological control agents have been introduced to the western United States, and are effective at reducing seed production (Mauer, et al. 1987).
Photo: Nebraska Department of Agriculture
Fig Buttercup/Celandine
Fig Buttercup/Celandine
Ranunculus ficaria
Description
Lesser celandine is an annual herbaceous plant that grows in early spring (Swearingen 1999). It has glossy, dark green, rounded leaves arranged in a low-growing rosette with both fibrous and tuberously thickened roots. The leaves appear in late winter and die back by early June. Bright yellow buttercup-like flowers bloom in March and April, held above the leaves. Seeds mature by May, but reportedly are rarely formed (Rhoads 1999). Vegetative reproduction is by small underground tubers and by axillary bulblets formed on the stems. Both tubers and bulblets are readily dispersed during flooding events (Swearingen 1999).
Habitat
Lesser celandine is characteristic of moist alluvial soils in forested floodplains. It also invades grassy meadows, roadsides, lawns, and less frequently drier soils of embankments and open woodlands (D. Snyder, personal observation). The earliest New Jersey collection was collected from ship ballast (see specimen citations).
Threats
The invasive nature of lesser celandine was first reported by Snyder (1987) who noted that it was “aggressive and spreads rapidly once established” and that it has “already become a serious pest in some areas of New Jersey.” Lesser celandine forms near monocultures of extensive acreage (Rhoads 1999; Snyder 1987) in the early spring. Because of its early emergence and aggressive nature, lesser celandine poses a serious threat to indigenous spring ephemerals (Rhoads 1999; Swearingen 1999). It has significantly altered the structure of natural plant communities.
Control
Small infestations can be dug up, taking care to remove all the tubers and bulblets, but for larger populations, digging may create too much soil disturbance (Swearingen 1999). Herbicides can be used as soon as the leaves appear, but before when indigenous plants begin to grow. Herbicides should be used very cautiously to avoid harming indigenous plant and amphibian populations.
Photo: Leslie J. Mehrhoff, University of Connecticut, Bugwood.org
Purple Loosestrife
Purple Loosestrife
Lythrum salicaria
Description
Purple loosestrife is a perennial herb, with square woody stems, that typically grows up to three or four feet in height, but under favorable conditions may grow up to 10 feet tall (Bender 1987; Swearingen 1998). The leaves are lance-shaped, and either heart-shaped or rounded at the base. They are arranged opposite or whorled in groups of three or four along the stem. In summer, plants produce large showy spikes of magenta or occasionally white or light pink flowers. Each flower has 5 to 7 petals. The fruit is a capsule containing minute (0.06 mg) seeds. A single mature plant may produce up to 2.7 million seeds (Gutin 1999). The seeds are mostly wind dispersed, but they can be transported on the feet of waterfowl or by other wetland animals. Seeds float and are also dispersed by water. Plants have strongly developed taproots (Bender 1987). Plants can spread by underground roots and shoots as well as by seed (Vermont IEPFSS 1998).
Habitat
Purple loosestrife occurs in wetland areas including cattail marshes, sedge meadows, and open bogs (Bender 1987). It often occurs along river and stream banks, and in disturbed wet areas. It can tolerate a wide range of soil conditions and up to 50 percent shade (Bender 1987). In New Jersey it occurs abundantly along the Delaware River and other river edges, lake and pond shores, salt and freshwater marsh edges, meadows, limestone fens, floodplain forests, and from disturbed areas such as ditches and filled wetlands (see specimens cited).
Threats
Once it becomes established, purple loosestrife displaces native vegetation through rapid growth and heavy seed production (Bender 1987). Uncontrolled, purple loosestrife eventually forms a near monoculture that alters the structure of natural plant communities and reduces biological diversity. Dense stands can change drainage patterns by restricting the flow of water (Colorado Division of Plant Industry 2000). Wildlife can be affected by the displacement of indigenous food items such as cattails and pondweed. Waterfowl are threatened by the loss of favorable habitat to purple loosestrife (Swearingen 1998). In 1995, the National Park Service determined that purple loosestrife was a potential threat to state listed endangered plant species, special concern plant species, and two globally rare calcareous riverside plant communities documented from the Delaware Water Gap National Recreation Area (Shank and Shreiner 1999). This lead to a joint effort between the New Jersey Department of Environmental Protection through its Office of Natural Lands Management and the National Park Service to qualify these threats. This was done by establishing baseline data on population dynamics and community composition which will allow future statistical comparisons to be made to assess the effectiveness of biological control agents introduced to control the further spread of purple loosestrife (Shank and Shreiner 1999). Several limestone fens, another globally rare plant community, are threatened by the invasion of purple loosestrife. These fens support a remarkably diverse assemblage of state and globally rare plant, animal, and insect species. In New Jersey, several populations of the federally listed bog turtle (Clemmys muhlenbergii) are threatened by loss of habitat through the invasion of purple loosestrife (J. Teasuro, pers. comm.). A population of the state listed endangered wiry panic grass (Panicum flexile) was lost when its open fen habitat was succeeded by a dense stand of purple loosestrife (D. Snyder, personal observation). The Nature Conservancy is attempting to control the spread of purple loosestrife in a limestone fen at their Johnsonburg Preserve, Warren County (A. Heasly, pers. comm.). The Fish and Wildlife service estimates that purple loosestrife costs about $45 million dollars a year in control costs and lost forage (USFWS 1998). Many cultivars of purple loosestrife have been developed and are sold as landscape plants. It is currently illegal in 13 states to purchase and plant purple loosestrife (Vermont IEPFSS 1998).
Control
Large populations are almost impossible to eradicate, and the best management strategy may be to contain the populations and try to limit seed production (Bender 1987). Herbicides should be used with caution given that loosestrife is restricted to wetlands, often covering extensive acreage. Hand-pulling before plants have set seed can be effective for small populations and isolated stems, as long as root fragments are completely removed. Uprooted plants and broken stems should be removed since stems can resprout. Biological control of purple loosestrife is being tested with six insect species, and three of these insects have been approved by the U. S. Department of Agriculture (Swearingen 1998). In New Jersey, biological control of purple loosestrife is currently underway in several state natural areas and wildlife management areas, federal wildlife management areas, and Nature Conservancy preserves.
Photo: John D. Byrd, Mississippi State University, Bugwood.org

GRASSES


Japanese Stiltgrass
Japanese Stiltgrass
Microstegium vimineum
Description
Japanese stiltgrass grows as an annual grass (Mehrhoff 2000) with a sprawling habit, and can reach heights of up to 3 feet (Swearingen 1998; TN EPPC 1998). It has thin, pale green, lance-shaped leaves, about 3 inches in length, that grow alternately along a branched stalk. The leaves have a silvery stripe of reflective hairs down the center of the upper leaf surface (Swearingen 1998). The stalk is distinctly divided by nodes, with the segments between the nodes flattened and widening toward the upper end (Smith 1998). The flowers bloom along a delicate spike that emerges from the stalk tips in late summer and early fall (Swearingen 1998). The seeds mature in mid to late fall, and can remain viable for more than five years in the soil (TN EPPC 1998). Plants spread locally by rooting at the nodes. Seed dispersal is by animals, water, or deposition with fill dirt (TN EPPC 1998). The report that there is a rhizomatous perennial form occurring in eastern North America (Ehrenfeld 1999), has been challenged by Mehrhoff (2000), who believes the report is based on misidentification of the indigenous grass, Leersia virginica L. The two species are vegetatively similar and grow in similar habitats, often growing in mixed populations (Mehrhoff 2000). Vegetative plants can be distinguished by the silvery stripe running along the middle of the leaves of Japanese stiltgrass, a character lacking in Leersia virginica. The two species are easily distinguished when in flower or fruit.
Habitat
In New Jersey, Japanese stiltgrass is found in a range of habitats, from wetlands to early successional fields and forested uplands (Hunt and Zaremba 1992). It reaches its greatest abundance in floodplain forests and moist soils over shale, diabase, and glauconite (D. Snyder, personal observation). Although it is a shade adapted species (Winter, et al. 1982), it also grows in full sunlight, especially in disturbed habitats such as roadsides, powerline right-of-ways, ditches, agricultural lands, lawns and gardens. It appears to favor soils that are moist, acidic to neutral, and high in nitrogen (Swearingen 1998).
Threats
Japanese stiltgrass alters the structure of natural plant communities and reduces biodiversity by displacing indigenous herbaceous vegetation through its dense growth, which rapidly forms monocultures that are sometimes acres in extent. Because of its rapid and dense growth, it alters light and moisture regimes and likely affects seed germination. Kourtev, et al. (1998) speculated that Japanese stiltgrass in association with Japanese barrberry (Berberis thunbergii) raises pH and reduces the organic horizons in soils.
Control
Prevent introduction of Japanese stiltgrass from invaded sites to adjacent natural areas by avoiding disturbance to vegetation and soil in the natural areas (Swearingen 1998). Small infestations can be hand-pulled, but pulling will have to be repeated until the seed bank is exhausted. Plants can be mowed when flowers are blooming, but before seed set. Herbicides can be effective, and should be applied before plants set seed (TN EPPC 1998). Herbicides should be used with caution, as they could harm indigenous co-occurring plants.
Photo: Chris Evans, River to River CWMA, Bugwood.org

Source: Snyder, David and Sylvan R. Kaufman. 2004. An overview of nonindigenous plant species in New Jersey. New Jersey Department of Environmental Protection, Division of Parks and Forestry, Office of Natural Lands Management, Natural Heritage Program, Trenton, NJ. 107 pages.