Aquatic Invasive Plants

Over the years, many plants and animals have been brought into the US either intentionally or as stowaways in cargo and materials. Without native predators, many of these species out compete native species or reproduce in such a large quantity as to cause environmental damage.

This page describes a number of the invasive plants which can be found in the Adirondacks.

More information about Adirondack invasive species can be found at the web site for the Adirondack Park Invasive Plant Program(APIPP). Some of the photos and descriptions have been copied from the APIPP web site.


Eurasian Watermilfoil

Eurasian watermilfoil (Myriophyllum spicatum) is an attractive plant with feathery underwater foliage. It was once commonly sold as an aquarium plant. Eurasian watermilfoil, hereafter called milfoil, originates from Europe and Asia, but was introduced to North America many years ago and is now found over much of the United States. This plant was introduced to the eastern United States at least as long ago as the 1940s, but it may have arrived as early as the late 1800s. The first known herbarium specimen of milfoil in Washington was collected from Lake Meridian near Seattle in 1965. By the mid 1970s it was also found in Lake Washington. During this same time period milfoil became established in central British Columbia and traveled downstream to Lake Osoyoos and the Okanogan River in central Washington. Now milfoil is found in the Columbia, Okanogan, Snake, and Pend Oreille Rivers and in many nearby lakes. In western Washington, the distribution of milfoil closely follows the Interstate 5 corridor. It is very apparent that milfoil has been spread from lake to lake on boat trailers.


Variable-leaf watermilfoil

Variable-leaf watermilfoil is a submerged perennial that looks like many native plants, including native milfoil species. It has 4-6 feathery leaves whorled around the stem, but some leaves can be alternating. Leaves are divided into 7-14 pairs of leaflets. Dense leaf arrangement gives this plant a bottle brush appearance. Stems are thick and reddish-brown. In mid to late summer, blade-like, serrated leaves with small, reddish pink flowers form an erect spike that emerges from the water.


Water chestnut

Water chestnut is a fast-growing, floating annual that can grow to 16 feet. It has feathery, submersed leaves and triangular, toothed, floating leaves that are glossy. Floating leaf stalks have visible bulbous bladders and commonly form rosettes. Flowers with four white petals normally bloom in July. The most distinctive trait of this plant is its thorny nutlets which mature in late summer. Reproduction occurs from these very sharp nutlets and from fragmentation of the rosettes.



Fanwort is a submersed, sometimes floating, but often rooted, freshwater perennial plant with short, fragile rhizomes. The erect shoots are upturned extensions of the horizontal rhizomes. The shoots are grass green to olive green or sometimes reddish brown. The leaves are of two types: submersed and floating. The submersed leaves are finely divided and arranged in pairs on the stem. The floating leaves, when present, are linear and inconspicuous, with an alternate arrangement. They are less than 1/2 inch long and narrow (less than 1/4 inch). The leaf blade attaches to the center, where there is a slight constriction. The flowers are white and small (less than 1/2 inch in diameter), and they float on the water surface (Gibbons 1993; Radford 1968; Orgaard 1991). Cabomba is a small genus of aquatic plants originating in the neotropics and adjoining warmer temperate zones. There is a great deal of vegetative similarity among the taxa, making the genus taxonomically difficult (Orgaard 1991).


Curly Leaf Pondweed

Both curly leaf and flat-stem pondweed grow entirely underwater except for the flower stalk which rises above the water. Curly leaf pondweed has distinctly wavy-edged, crispy olive-green to reddish-brown leaves. It usually grows early in spring and dies back in summer. The leaves of flat-stem pondweed are long and narrow with smooth edges and the sharp-edged stem is flat and about the same width as the leaves.


European Frogbit

European frog-bit is an invasive aquatic plant native to Europe and parts of Asia and Africa. In 1932 the plant was brought from Europe to the Central Experimental Farm in Ottawa for possible commercial use as an ornamental plant. In 1939 it was found in the Rideau Canal. Since then it has spread to several rivers, Lake Ontario, Lake Erie and other inland waters


Yellow Floating Heart

Yellow floating heart was introduced as an ornamental aquatic plant from eastern Asia. It is a floating-leaved plant and is generally somewhat larger than America's native floating hearts. Its flower is yellow. It has adventitious roots along an underwater stem.


Brittle Naiad

Najas minor, known as Brittle Naiad or Brittle Waternymph, is an annual aquatic plant, a submersed herb, native to Europe, but known to be an invasive species in North America. This plant prefers calm waters, such as ponds, reservoirs, and lakes, and is capable of growing in depths up to 4 meters.


Brazilian Elodea

Brazilian elodea (Egeria densa) is an attractive, robust plant well-suited to aquarium life. Up until 1996 it was commonly sold in Washington pet stores under the name "anacharis."  It was also sold in plant nurseries as an "oxygen" plant. Because of its invasive properties that allow it take over in waterbodies where it is introduced, it is no longer being sold in Washington.



Hydrilla is a submersed plant. It can grow to the surface and form dense mats. It may be found in all types of water bodies. Hydrilla stems are slender, branched and up to 25 feet long. Hydrilla's small leaves are strap-like and pointed. They grow in whorls of four to eight around the stem. The leaf margins are distinctly saw-toothed. Hydrilla often has one or more sharp teeth along the length of the leaf mid-rib. Hydrilla produces tiny white flowers on long stalks. It also produces 1/4 inch turions at the leaf axils and potato-like tubers attached to the roots in the mud.


Japanese Knotweed

Japanese knotweed is a fast-growing, herbaceous perennial with jointed, hollow stems and alternate, leathery leaves that are broadly ovate. A cascade of white flowers blooms in August, and dormant reddish stems are visible in winter. Giant knotweed, Fallopia sachalinensis, is another nonnative knotweed in the Park.



Black and pale swallow-worts are herbaceous perennial, twining vines. Leaves are opposite and glossy. Small maroon to pale pink flowers are present in late May through late July. Seed pods are smooth, slender, and pointed and are abundant in late summer. Pods split open, releasing innumerable downy seeds that are easily carried miles by wind.


Oriental Bittersweet

Oriental, or Asiatic, bittersweet is a perennial, deciduous vine that can grow to 60 feet. Stems have a dark brown, striated bark. Elliptic to ovate leaves are alternate and spiral evenly around the stem. Axillary flowers bloom in May to early June yielding bright, reddish-orange fruit in the fall. Oriental bittersweet can be confused with American bittersweet, which has a terminal inflorescence and is native.


Purple Loosestrife

L. salicaria, a plant of European origin, has spread and degraded temperate North American wetlands since the early nineteenth century. The plant was introduced both as a contaminant of European ship ballast and as medicinal herb for treatment of diarrhea, dysentery, bleeding, wounds, ulcers and sores.


Yellow Iris

Iris pseudacorusis a wetland plant that is especially showy during its short blooming period. This good-looking plant has been transplanted into well-watered gardens all over the world and has widely escaped; it is also used in sewage treatment, and is known to be able to remove metals from wastewaters. Like cat-tails, yellow iris colonizes into large numbers, forming very dense monotypic stands, outcompeting other plants.


Garlic Mustard

Garlic mustard was first recorded in the United States around 1868, from Long Island, New York, and was likely introduced by settlers for food and medicinal purposes.  Garlic mustard has displaced vast areas occupied by native spring wildflowers like spring beauty (Claytonia virginica), wild ginger (Asarum canadense), bloodroot (Sanguinaria canadensis), trilliums (Trillium species) and toothworts (Cardamine). Three native butterfly species, the West Virginia white (Pieris virginiensis), mustard white butterfly (Pieris oleracea), and the falcate orange-tip (Anthocharis midea annicka), are especially impacted when garlic mustard displaces toothworts, its host plants. Chemicals in garlic mustard are toxic to the larvae of the native butterflies. Other chemicals have been found to affect mychorrhizal fungi associated with native trees, resulting in suppression of native tree seedling growth.


Common Reed Grass

Common reed is another very large grass plant, native to Florida. It is occasionally found growing in rivers, lake margins, fresh or brackish marshes, and wet, disturbed sites from the central and southern peninsula to the panhandle of Florida (Wunderlin, 2003). Phragmites australis blooms in the fall and is used by people and wildlife in many ways. Phragmites easily might be confused with the non-native invasive, Neyraudia.


Giant Hogweed

Giant hogweed (Heracleum mantegazzianum) is a Federally listed noxious weed. Its sap, in combination with moisture and sunlight, can cause severe skin and eye irritation, painful blistering, permanent scarring and blindness. Contact between the skin and the sap of this plant occurs either through brushing against the bristles on the stem or breaking the stem or leaves.


Wild Chervile

Wild Chervil, Anthriscus sylvestris (L.) Hoffm., is a weed belonging to the parsley family (Apiaceae) and is becoming a serious problem in hay fields and pastures in central Vermont. It's three to four foot heights, fern-like leaves and white flowers arranged in a compound umbel pattern are quite pronounced during late May to early July and are commonly found along roadsides and in meadows in central Vermont.

Terrestrial Invasive Plants

Updated 3/20/2018