Family: Alismataceae
  Cham. & Schlecht   (long-lobed arrowhead)

Field Description: Emersed annual herb standing erect to 50 cm with broadly ovate leaves on stout spongy petioles.  Flowers in whorls varying up to 12, having white petals, sometimes with a yellow hue and a purple spot at base.
Habitat: Shallow waters of streams, lakes, swamps and canals.
Native Range: Temperate and subtropical South America.
Nonindigenous Range: Very occasional species persisting in few locations in the United States. Only known in the Mid-Atlantic States from New Jersey’s Lower Hudson River drainage and may not represent a persisting population.

NJ 1929

Comments: Still available as a water garden ornamental which may serve as an outlet for escapes to new locations.

Family: Amaranthaceae
  (Mart.) Griseb.  (alligatorweed)

Field Description: Emersed perennial herb with decumbent hollow stems rooting at the nodes and growing to1 m long.  Leaves are opposite, sessile and elliptic.  The inflorescence is a clover-like head on a short stalk, lacking petals but with 5 white sepals.
Habitat: Moist or wet sites, most often along ponds, lakes, streams, canals and ditches.
Native Range: South America.
Nonindigenous Range: Well established and common mainly in the southeastern and Gulf coastal United States. Collected in the Mid-Atlantic States from eight coastal counties of Virginia.  Populations inhabit ditches, lakes, and swampy areas in these counties and are persisting in abundant local colonies. 

VA 1956

Comments: Viable seed is not known in the United States where reproduction is entirely vegetative. The northern distribution of alligatorweed is probably limited by the cold sensitivity of above ground vegetation.

Family: Brassicaceae
  Ait. f.  (watercress)

Field Description: Submersed to floating or emersed aquatic perennial usually 10 - 45 cm tall with smooth, freely rooting stems that appear succulent.   Leaves are alternate and pinnately compound with 3 -11 ovate to oblong leaflets.  White flowers in racemes form narrow pods containing two rows of seeds. 
Habitat: Cold water springs and fast flowing streams.
Native Range: Europe.
Nonindigenous Range: Common and established in the United States excepting Alaska and Hawaii.  Long time established in the Mid-Atlantic States at millponds, local creeks, swamps and lakes.  Collected from New Hampshire, 1965, at two separate locations in the Piscataqua-Salmon Falls drainage.  Known from at least five towns in southeastern Vermont. Common throughout the state of Rhode Island in all counties and in most townships.  In Maine, populations exist in Oxford, Somerset, Hancock and York counties.

VA WV  MD  DE  PA  NJ  NY  CT   RI  MA  VT  NH  ME 1892 1944* 1905 1894 1879 1983* 1969 1831 1952* 1944* 1944* 1944* 1932

Comments: Cultivated for its edible greens since early colonial times.  Apparently has little impact on natural communities and is not considered a management concern in the Northeast, however, in arid regions of western states this species can become weedy to alter function and flow in shallow, mountain streams.  Synonym: Rorippa nasturtium-aquaticum

  (L.) Bess. (amphibious yellowcress)

Field Description: Perennial herb often growing emersed and erect to 10 cm with hollow stems.  Alternate, lanceolate leaves are undivided and roughly dentate. Flowers are golden yellow, with yellow sepals that are at least half as long as the petals.  The fruit (3 - 6 mm) is an oblong to obovate silique with a straight to slightly curved beak (1 - 2 mm). The silique splits into open halves and contains one row of seeds that are large in proportion to the silique.     
Habitat: Swamps and shallow waters of lakes and ponds.
Native Range: Europe.
Nonindigenous Range: Restricted in the United States, to occassional locals in the Mid-Atlantic States. Established in Connecticut in the Saugatuck River drainage and in Maine, at Lake Androscoggin, and in Vermont near the mouth of the Missisquoi River.  Although infrequent, it often forms dense beds and may be more prevalent in the region, perhaps just overlooked.

NY CT MA VT ME 1993* 1957* 1991* 1996* 1957*

Comments:  Sometimes confused with Armoracia (lake cress) for the yellow flowers, but is distinguished by its elongated pods which have a central partition that is lacking in lake cress.

Family: Butomaceae
  L. (flowering rush)

Field Description: Perennial aquatic herb with fleshy rhizomes and linear, basal leaves that grows either lax and submersed or emersed and upright to reach 1 m in height.  Flowers pink, in terminal umbels of up to 50 on long, naked stalks.  Fruits multiple in whorls with numerous seeds.
Habitat: Stream banks, marshes, pond and lakeshores.
Native Range: Temperate Eurasia.
Nonindigenous Range: Occasional in the northern United States west to Washington. Infrequent in the Mid-Atlantic States yet well established in major water bodies such as Lake Erie, Lake Champlain, and the St. Lawrence River.  The recent, sole record for Maine is from a pond near Hooper Brook Inlet in the Lower Androscoggin drainage.

PA  NY  CT  VT ME 1941 1929 1943 1927 1999

Comments: Cultivated as a decorative water garden plant.  Produces dense stands; use of herbicides has had limited success. Means of dispersal unknown.

Family: Callitrichaceae
  Scop.  (pond water-starwort)

Field Description: Submersed to floating or amphibious herb.   Rooted shoots grow to the surface to form floating rosettes with tiny, opposite leaves, up to 10 mm wide, that are entire, yet diverse in shape.  Monoecious plants form tiny flowers with 2 whitish basal bracts and round fruits with marginal wings.
Habitat: Static or flowing water of ponds, streams, marshes and ditches.
Native Range: Europe and northern Africa.
Nonindigenous Range: Established along the West Coast and in a few other regions of the United States. Common and locally abundant from Virginia north to Massachusetts in the Mid-Atlantic States. Locally common and established almost throughout the state of New Jersey, where it is found in 16 counties.  Persisting in Pennsylvania since the early 1900s where it now exists in 15 counties in the southeastern region of the state.

VA MD  PA  NJ  NY  CT  MA 1952 1942 1911 1885 1861 1994 1911

Comments: Reproduces sexually by seed and clonally by fragmentation to form dense mats. The species is a prolific seed producer, although seed production may not occur in all populations. Unlikely to be confused with any other plant, except for several native species of Callitriche, which it closely resembles and can only be distinguished by the fruits. Callitriche stagnalis produces globose fruits (1.5 x 2 mm) that are distinctly winged (0.1 mm wide) along the margins. Thought to be introduced in dry ballast during the late 1800s.

Family: Commelinaceae
  (Hassk.) Hand.-Maz. (marsh dewflower)

Field Description: Emergent aquatic annual herb with trailing, mucilaginous stems rooted in water up to 1.5 m deep.  Leaves alternate, simple, lance-shaped, 3-6 cm long by 1 cm wide.  Flowers with 3 petals, pink to lavender or white to blue, axillary, either solitary or 2-4 in a raceme. Fruit an oval capsule bearing many fertile seeds.
Habitat: Marshes, ditches and shallow lake shorelines.
Native Range: East Asia.
Nonindigenous Range: Established and becoming more abundant in the southeastern United States where its range is increasing in the Mid-Atlantic States. Key populations occur in marshes of the Patuxent National Wildlife Refuge, Maryland and in the Mason Neck National Wildlife Refuge, Virginia. Also found in both the James and Potomac Rivers, Virginia. Known from all three counties in Delaware, both from the Piedmont and Coastal Plain where it is found in both tidal and non-tidal waterbodies, probably since the late 1980s (Keith Clancy, Delaware State University, pers. comm.).

VA MD  DE 1939 1949 1993

Comments: Introduced with early rice farming to South Carolina in 1935 (Dunn and Sharitz, 1990). Escaping cultivation practices to become a competitive plant that forms dominant colonies in natural areas.

Family: Iridaceae
  L. (yellow iris)

Field Description: Hearty emergent or shoreline perennial about 1.5 m tall with thick, tuberous rhizomes.  Leaves long, flat and sword-like with upper and lower surfaces identical.  Yellow flowers on erect stalks have sepals (called “falls”) faintly etched in brown or purple. Fruit is a large cylindrical capsule containing many flattened, fertile seeds.
Habitat: Shallow waters of swampy woodlands, marshes, meadows and stream banks.
Native Range: Europe and British Isles, northern Africa and the Mediterranean region.
Nonindigenous Range: Established and widely distributed in the United States, notably along channelized river systems and in important natural public lands in the western states. Spreading extensively to wet areas in over 45 drainages in the Mid-Atlantic States, where plants have been found in the wild for close to 140 years.  Recorded from the Parker River National Wildlife Refuge, Massachusetts. Still reaching new states by the 1990s, where escapes spread locally from cultivation.   Plenty of territory remains to be affected by new suburban settings.

VA  WV  MD  DE  PA  NJ  NY  CT  RI  MA  VT  NH  ME 1992 1996* 1969 1895 1923 1990* 1868 1903 1952* 1884 1996* 1980 1974

Comments: Invasive for its robust, drought tolerant rhizomes that spread radially to produce large clonal populations that grow to the exclusion of native marsh plants. Both rhizomes and seeds may be transported downstream during floods.  Poisonous and listed as an injurious weed in western states.  Continues to be planted for erosion control and sewage treatment.  Burning is not recommended for control because of its strong tendency to resprout from rhizomes.

Family: Lythraceae
  L. (purple loosestrife)

Field Description: Erect, emergent perennial herb with stout, tough, nearly square stems reaching over 1 m tall.  Fifty stems may arise from a single mature rootstock. Leaves are sessile and hairy with rounded bases that practically surround the stalk. Leaves opposite to alternate or arranged in whorls. Flowers reddish (mauve) purple in showy spikes.  Seeds produced in capsules.
Habitat: Prefers moist or saturated soils of meadows, marshes, lakeshores and river margins.
Native Range: British Isles, Europe and Eurasia including parts of Russia.
Nonindigenous Range: Unevenly distributed across the United States, more frequently in the cooler climates. Common and aggressive in the Mid-Atlantic States where it is well established in over 60 drainages, and continues to expand in range. Key populations exist in the Parker River National Wildlife Refuge, Massachusetts and in the Montezuma National Wildlife Refuge, New York. New to Virginia in 1996 at the James River, Lower Chesapeake, and Upper Clinch River drainages.

VA  WV  MD  DE  PA  NJ  NY  CT  RI MA  VT  NH  ME 1996 1858 1896 1866 1852 1864 1843 1895 1905 1831 1898 1875 1954

Comments: Produces monotypic, dense stands in wet habitats that displace native plant communities important for animal habitat.  A copious seed producer, output depends on age, size, and vigor.  A single plant is capable of producing more than 2 million seeds. Seeds spread by wind, water, or waterfowl and can remain dormant for 2-3 years until environmental conditions become favorable. Certain species of weevils and leaf-eating beetles are being used as biological control agents.  Still sold as an ornamental garden plant.  

Family: Marsileaceae
  Mett.  (nardoo)

Field Description: Aquatic to amphibious fern growing from creeping, fleshy, rooted rhizomes.  Four-leaf clover-like leaves uniquely two toned in color, lighter in the center and darker towards the margins, often with a thin red-brown band delineating the color zones. Leaves glabrous, land leaves 2-3 cm broad.  Floating leaves larger, to 6 cm broad, attached to petioles as long as 1 m.  Petioles inflated at the apex to promote buoyancy of floating leaves. Sporocarps ovoid with blunt tips, completely lacking teeth, borne on short stalks that arise from the junction of the petiole and rhizome, initially covered in thick, woolly hair.
Habitat: Heavy clay to sandy substrates of permanent lakes and seasonal ponds, fringing shorelines and extending into deeper water.
Native Range: Australia and New Caledonia.
Nonindigenous Range: Newly introduced to the United States where locally abundant populations over winter in Oklahoma, Mississippi, Alabama, Georgia, Florida, and South Carolina. First recorded from the Mid-Atlantic States in southeastern Virginia.

VA 1997

Comments:  Marsilea mutica is an invasive colonizer and extensive grower that readily adapts to environmental change.  Plants demonstrate few habitat preferences outside of full sun and wet periods. Unlike Marsilea quadrifolia, M. mutica appears well suited to more southern ranges in the United States. In its native range, M. mutica depends on dormant vegetative propagules (rhizomes) to persist through interludes of water recession and low temperature. In the U.S. the importance of sporocarps in reproduction and in dispersal is unknown.  The recent influx to North America is probably through horticultural escapes. 

  L. (European water-clover)

Field Description: Aquatic to amphibious fern from creeping, fleshy, rooted rhizomes.  Four-leaf clover-like leaves monochromatic green, downy on first appearance (as fiddleheads) becoming glabrous when mature. Land leaves 1.5 - 4 cm broad. Sporocarps bear a single posterior tooth, are covered in hair that later sheds, and borne on short stalks that arise 1 – 12 mm above the junction of the petiole and rhizome.  In wet conditions, male and female spores germinate and cross-fertilize to produce new plants.
Habitat: Wet conditions of slow-flowing rivers and streams, muddy shorelines to roadside ditches.
Native Range: Europe.
Nonindigenous Range: Established in the United States for more than a century, predominantly in the northeastern portion of the Mid-Atlantic States where occurrence remains occasional. United States’ populations do not extend south of Maryland, Kentucky or Missouri. Massachusetts has the most extensive introductions including long-time documented sites in the Charles, Concord, Sudbury and Connecticut rivers. 

MD  PA  NJ  NY  CT MA  ME 1909 1894 1929 1893 1860 1868 1986*

Comments: Becomes weedy by producing monotypic vegetative stands that over winter by underground rhizomes. While plants mainly reproduce clonally, new populations may develop from hardened sporocarps that lie dormant in the substrate for decades. As an invasive weed, Marsilea quadrifolia generally carries little consideration. Distinguish M. quadrifolia from the newly introduced M. mutica by M. quadrifolia having a solid green leaf color, peduncles that attach higher up on the petiole and sporocarps bearing a tooth.

Family: Nelumbonaceae
  Gaertn. (sacred lotus)

Field Description: Perennial aquatic herb with large, orbicular leaves that arise directly from thick rhizomes embedded in the substrate.  Early in the season, leaves float flat on the water surface. Later in summer leaves emerge on petioles above the surface and become trumpet-like in shape.  Flowers solitary and pink, forming woody, fruiting receptacles that contain seeds in pitted cavities. 
Habitat: Prefers calm waters of ponds, lakes, streams and marshes.
Native Range: Southeastern Asia and Australia.
Nonindigenous Range: Established scarcely in the southeastern United States likely as independent introductions from cultivation. Collected but status unknown in several Mid-Atlantic States.  Earliest and only known record from West Virginia was collected from the Lower Kanawha drainage.  It has not been verified if specimens from West Virginia, Maryland, New York and New Jersey have persisted to become established.

WV MD  NJ  NY 1984 2003* 1958* 2003*

Comments: Spectacular ornamental cultivated in water gardens that may be intentionally introduced due to its large showy flowers. Readily distinguished from the native yellow- flowered American lotus (Nelumbo lutea).

Family: Onagraceae
  (Hook. & Arn.) Zardini, Gu & Raven (Uruguay seedbox)

Field Description: Floating to emersed perennial aquatic herb growing rooted in water to 1.8 m deep or in wet soils.  Aquatic plants in deep water appear as floating rosettes with more rotund leaves. Emergent stems are highly pubescent with lance shaped, alternate leaves. Bright yellow flowers are solitary at the leaf axils.  Seeds are enclosed in a cylindrical, hairy capsule.
Habitat: Marshes, swamps, ponds and lakes, ditches and small streams.
Native Range: South America.
Nonindigenous Range: Probably introduced in the southeastern United States and along the West Coast.  Established yet infrequent in the Mid-Atlantic States where few populations exist. The earliest record from Pennsylvania was from the Schuylkill drainage where later occurrences were also found, and the only other population for the state was found in the Lower Delaware drainage. Known from unspecified locations in swamps and ponds in southern New York.

VA  WV  DE  PA  NY 1990* 1996* 1993 1941 1991*

Comments: Potentially invasive becoming problematic by forming dense, floating mats in ditches and streams. Reproduction by prolific seed production, vegetative fragmentation and rhizome spread. Water garden industry sells this species under false names.  Earlier known as Ludwigia uruguayensis.

Family: Poaceae
  (Hartman) Holmb. (reed mannagrass)

Field Description: Perennial rhizomatous aquatic grass with more or less erect, leafy stems reaching 2.5 m.  Leaves flat to half folded at maturity, margins endowed with tough, short hairs that are rough to the touch. Inflorescence is an open panicle producing small, smooth brown seeds.
Habitat: Primarily found in marshes, swamps and wetlands but can exist along shorelines of lakes and ponds.
Native Range: Eurasia.
Nonindigenous Range: Uncommon in the United States where it was first recorded in 1975 in the Upper Fox drainage of Wisconsin, appearing again four years later in the nearby Pike-Root drainage. The remaining occurrences lie in the Mid-Atlantic region in Massachusetts at the Ipswich River Wildlife Sanctuary, where populations at four sites appear to be under management control.

MA 1990

Comments: Making its first appearance in North America in 1940 in Ontario, Canada.  This species impacts wetland ecosystems by forming dense monospecific stands. It is a poor food source and provides unfavorable nesting substrate for wildlife.  Reproduces vegetatively by rhizomes.  Seed viability has not been studied in the United States.   Has the potential to become a troublesome wetland plant where introduced.

Family: Scrophulariaceae
  (L.) Kuntze  (mud mat)

Field Description: Minute aquatic to amphibious perennial herb recognized as unusual, bright green patches on muddy substrate of littoral zones in full sun. Creeping rhizomes support tiny (1-2 cm) leaves, opposite and spatulate in shape.  Flowers are bell-shaped, pastel colored and produced on short stalks when water recedes. Closed, self-fertilizing flowers, called cleistogams are produced underwater among the roots. Seeds are produced in capsules.
Habitat: Prefers shallow waters, swamps, marshes, backwaters and inundated areas.
Native Range: New Zealand, Australia, India and eastern Africa.
Nonindigenous Range: Sparingly distributed in the United States, recorded only from 6 sites in 2 adjacent drainages in the Mid-Atlantic States of New Jersey and Pennsylvania.   First collected from a reservoir in Middlesex County, New Jersey, where plants are abundant in shallow areas around the impoundment. Later found in Mercer, Monmouth, and Ocean counties, New Jersey. First appeared in Pennsylvania at Lake Galena in the Crosswicks-Neshaminy drainage where the populations appear to fluctuate along the shoreline.

PA  NJ 1995 1991

Comments: Densely mat forming in shallow waters.  Glossostigma resembles the native Limosella (mudwort) species and may also be confused with emergent leaf forms of some members of Utricularia (bladderwort).  Sepal lobes, petal lobes and stamens are used to separate Limosella from Glossostigma.   

  L. (European brooklime)

Field Description: Emersed perennial aquatic herb with creeping, branching stems. Leaves short, petiolate, opposite, shiny, broadest near the middle, and scalloped at the margins.  Axillary flowering racemes of 10-30 bright blue flowers.  Fruit a many-seeded orbicular capsule.
Habitat: Prefers muddy edges of cold, oxygen-rich waters, but found in wetlands, floodplains, lakes and rivers.
Native Range: Europe, the Middle East, and Asia.
Nonindigenous Range: Infrequent in the United States, more common in the Great Lakes and Mid-Atlantic States where limited colonies are scattered. Also recorded from unspecified locals in Maryland, Connecticut, and Massachusetts. Occurring along the Delaware River in Pennsylvania.  Status of a single, early collection could not be verified in Hudson County, New Jersey.

WV  MD  PA  NJ  NY  CT  MA  ME 1931 2003* 1891 1876 1880 2003* 2003* 1937

Comments: Apparently posing little threat to aquatic communities. May be confused with native species of Veronica, especially V. americana that grows in similar habitats, yet has leaves broadest at the base. Reproduces by seed and through fragmentation. Reportedly can form large stands.