AQUATIC INVASIVE PLANTS FACT SHEETS

Prepared by:

Nez Perce Tribe Department of Fisheries Resource Management Watershed Division
Mr. Richard L. Christian, Project Leader P.O. Box 909 / 500 Main Street Joseph, OR (541) 432-2506

April 13, 2010

Aquatic Invasive Plant List
Common Name Flowering Rush Hydrilla Eurasian Watermilfoil Common Reed African Elodea or African Waterweed Rock Snot or Didymo Yellow Floating Heart Water Hyacinth Giant Salvinia Yellow Flag Iris European Water Chestnut European Frogbit Carolina Fanwort Feathered Mosquitofern Parrot Feather Watermilfoil Twoleaf Watermilfoil White Watercress Narrow Leaf Cattail Scientific Name Butomus umbellatus Hydrilla verticillata Myriophyllum spicatum L. Phragmites australis ssp. australis Lagarosiphon major Didymosphenia geminate Nymphoides peltata Eichhornia crassipes (Mart.) Solms Salvinia molesta Iris pseudacorus Trapa natans L Hydrocharis morsus-ranae Cabomba caroliniana Azolla pinnata R. Br. Myriophyllum aquaticum Myriophyllum heterophyllum Michx. Rorippa nasturtium-aquaticum Typha angustifolia USDA Code BUUM HYVE3 MSP2 PAHU7 LAMA15 NA NYPE EICR SAMO5 IRPS TRNA HYMO6 CACA AZPI MYAQ2 MYHE2 RONA2 TYAN Page 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

FLOWERING RUSH
(Butomus umbellatus) Family: Butomaceae

Flowering rush, also known as grassy rush and water gladiolus, is not a true rush species. Currently there are no known sites of flowering rush located in Oregon. It has been found on the Snake and other regions of the Columbia River system are considered highly susceptible to invasion. Most western infestations are a sterile triploid form. However, there is still considerable risk of the diploid form infestations, as the plant is still being sold online and by pond plant retailers.

Description This weed is distinctive and easy to identify when flowering, difficult when
not in flower. It is a tall plant growing to a height of 1.5 meters in marshes and in aquatic habitats. The plant crown is topped by an umbel of showy-white or pink flowers that emerge in late summer to early fall. Leaf stems are triangular in cross-section. Flowering rush reproduces both asexually by rhizomes and bulblets and sexually through seed production. Moving water is the predominant dispersal mechanism for localized as well as long-distant weed movement, human activities and wildlife also contribute.

Impacts: This plant has the potential to invade
and disrupt native marshlands. In the lower Columbia, it may compete strongly with reed canary grass. Evidence of economic damage is now emerging in the western United States. Unlined irrigation canals are becoming clogged as well as drainage ditches. Maintenance of these structures is expensive. Public and private boat access is now being impeded at some locations in Idaho (Rice 2008). It is unclear at this time of the effects on fishing access and success. Shallow lakes could become seriously infested and rendered unfishable. Reservoirs with variable water levels provide great habitat for this species.
Images courtesy of Leslie J. Mehrhoff, University of Connecticut, Bugwood.org and FoxyIslandWalks.com.

1

HYDRILLA
(Hydrilla verticillata)

weeds.hotmeal.net

Hydrilla was imported from Asia in the 1950’s for use in aquariums and was first introduced to the wild in Florida. Now established in several states including Washington and California. Clogs irrigation and drainage canals, interferes with recreation, displaces native vegetation and damages sportfish populations. Transported on boats and trailers.

Description: Perennial aquatic plant. Grows rooted to the bottom with long stems that
reach water’s surface. Can be monoecious or dioecious. Leaves are 1/16 to 1/8 inch wide, 1/4 to 3/4 inch long and occur in whorls of five. Small, axillary leaf scales are found next to the stem and inserted at the base of the leaf, a character that distinguishes hydrilla from other family members. The nut-like turions (tubers) are a key identifying feature.

Impacts: Hydrilla is the most
serious threat to aquatic ecosystems in temperate climate zones. Dense stands of hydrilla provide poor habitat for fish and other wildlife altering water quality by raising pH, decreasing oxygen, and increasing temperature. Stagnant water created by mats provides good breeding grounds for mosquitoes. Hydrilla interferes with recreational activities such as swimming, boating, fishing, and water skiing and will clog irrigation ditches and intake pipes. 2

EURASIAN WATERMILFOIL
(Myriophyllum spicatum L.)

www.ecy.wa.gov/.../plants/weeds/images/fish2.jpg

Initial introduction is not certain, but it has been suggested that it was accidently introduced to Chesapeake Bay in the 1800s from Eurasia or northern Africa, probably with ship ballast. Common throughout western Oregon and the Columbia Basin. It is not known to be in Wallowa County, but it is abundant in Umatilla and Morrow Counties.

Description: Perennial, aquatic plant. Purplish red branching stems grow up to five feet
long. Feather-like leaves in whorls of four at each node. Male flowers purplish and appear at the end of the flowering stem. Lower, whitish flowers are female. Determination between these natives and Eurasian water milfoil is difficult to do without flowers, but typically leaves of EWM have more than 14 leaflet pairs (28 individual leaflets) and the leaves are very lax, collapsing around the stem when taken out of the water.

Impacts: Eurasian watermilfoil has significant
economic impacts to waterways, irrigation ditches, and drainage canals where it can inhibit flow and increase maintenance costs. It is also a pest of rivers, lakes and ponds were it reduces water quality, impeded recreation and boat access and have adverse impact to fish habitat. Elevated nutrient levels created by erosion, fertilizers or urban effluent create a rapid growth response that can render a waterway clogged within a short period of time. Expensive control projects frequently target this plant across North America.
weeds.hotmeal.net/weeds/Eurasian_Watermilfoil.jpg

3

COMMON REED
(Phragmites australis ssp. australis)

Also known as giant reed, phragmites, giant reedgrass, Roseau cane and yellow cane, common reed has been widely introduced and is naturalized in the United States. Large populations of Phragmites can be observed at Klamath Lake, Summer Lake, Garrison Lake, John Day River, in North Portland adjacent to Smith and Bybee Lakes, and along the Columbia River, but no determination has yet been made regarding native or introduced lineages. Of these populations the Ft. Stevens and Smith-Bybee are currently known to be introduced.

Description: A large, perennial, clonal grass species with
creeping rhizomes and stolons, and terminal, plume-like flowering stalks. Known This plant has woody hollow stems that can grow 1-4 meters tall with stem diameters of 0.5-1.5 cm. Leaves are 1540 cm long with an open leaf sheath. Phragmites grows in a wide range of sites that hold shallow water, including roadside ditches, marshes, swamps, brackish estuaries, and alkaline wetlands. Reproduction is primarily vegetative, through an extensive network of rhizomes, which can grow horizontally up to 1.8 m per year depending on the climate. Differences between the native and invasive phragmites can be subtle and may partially depend on ecological conditions. ODA recently posted this link to help folks to determine the differences between native and non-native (http://www.oregon.gov/ODA/PLANT/WEEDS/phragmitesidentification.shtml).

Impacts: Phragmites dominated areas exclude large wading birds, increases land
elevation, reduces habitat for important fish species, disrupts trophic transfers, blocks fish passage, reduces refuge by steepening creek banks. In addition, Phragmites can have adverse impacts on waterfront property values and recreation such as hunting and fishing. Disturbances or stresses such as pollution, dredging, and increased sedimentation favor invasion, and spread of non-native Phragmites.
James H. Miller, USDA Forest Service

4

AFRICAN ELODEA OR AFRICAN WATERWEED
(Lagarosiphon major) It is believed that this plant was in New Zealand for some time before it was recognized as a plant distinct from Elodea canadensis in the 1950s. By the time it was recognized, Lagarosiphon major was already a major weed there.

Description: As a submersed, long-stemmed plant
having many small narrow leaves, Lagarosiphon major might be confused with three other plants in the U.S. As chance would have it, two of these three other plants are themselves also not native to the U.S.; however they are here, whereas Lagarosiphon is not (early 2008). This plant is rooted in the hydro-soil by numerous thread-like unbranched roots. The stems are submersed, brittle (3mm or 1/8 in) growing to 20 feet long, branching every 10-to12 nodes. The 3-veined with visible midvein leaves are submersed, greatly recurved and alternate spirally along the stem (16 mm (1 in.) long by 2 mm (1/16 to 1/8 in.) wide). The flowers are tiny transparent to white or pinkish. African waterweed will grow in lakes, rivers, streams and ponds, oligotrophic to eutrophic. It prefers cooler waters and is winter hardy (optimum temperature, 20-23o C (68-74oF); maximum temperature, 25o C (77o F)). The determinant of its maximum depth (about 7 m) is pressure (in non-light-limited environments).

Impacts: Happily, Lagarosiphon major does not
yet occur in the wild in the United States, as 2008, so far as is known. However, experts have reason to believe that should this plant be introduced to the U.S., the resulting problems could be as consequential as those caused by another plant in the Hydrocharitaceae family, hydrilla (Hydrilla verticillata).

5

ROCK SNOT OR DIDYMO
(Didymosphenia geminata) The native distribution of D. geminata is the cool temperate regions of the Northern Hemisphere, including the rivers of northern forests and alpine regions of Europe, Asia and parts of North America. Until its recent discovery in New Zealand, where it was introduced, it was never previously found in the Southern Hemisphere. The distribution of didymo in the last two decades appears to be gradually expanding outside its native range. The exact pathway of introduction is unknown, but it spreads easily through contaminated boats and fishing gear.

Description: Didymosphenia geminata is a
diatom, which is a type of single-celled algae unique for their silica (SiO2) cell walls. The life history of diatoms includes both vegetative and sexual reproduction, though the sexual stage is not yet documented in this species. Although it is symmetric only along the apical axis, typical of gomphonemoid diatoms, it is a cymbelloid, which are typically symmetric along both primary axes. Cells contain a raphe, which allows them to move on surfaces, and an apical porefield, through which a mucopolysaccharide stalk is secreted. The stalk can attach to rocks, plants, or other submerged surfaces. When the diatom cell divides, through vegetative reproduction, the stalk divides too, eventually forming a mass of branching stalks. The nuisance build-up is not the cell itself, but their massive production of extracellular stalks. Extracellular polymeric substances (EPS) that form the stalks are made primarily of polysaccharides and protein, forming complex, multi-layered structures that are resistant to degradation. The microscopic algae can be spread in a single drop of water.

Impacts: Didymosphenia geminata, if it overgrows, it can form large mats on the bottom
of lakes, rivers and streams. It is not considered a significant human health risk, but it can affect stream habitats, disrupt ecological processes, causing a decline in native plant and animal life, and make recreational activities unpleasant. It is considered a nuisance organism or invasive species. 6

YELLOW FLOATING HEART
(Nymphoides peltata) Other common names: Asaza, entire marshwort, floating heart, and fringed water lily.

Yellow Floating Heart was introduced to the U.S. as an ornamental water plant from the Mediterranean area. There are several known sites in Oregon in the recent past. One site was found in Washington County (2004), Lane County (2005), Douglas County (2007), Lane County (2007), and Jackson County (2008). It appears that this plant is spreading in the past few years.

Description: Aquatic perennial. Grows rooted to
the bottom in water depths of 2-13 feet. Floating leaves heart-shaped to circular, 1 to 4 in long, purplish underneath with slightly wavy margins. Leaves attached to long stalks that arise from creeping underwater rhizomes. Flowers bright yellow, 5-petaled, and 1 to 1 1/4 inch in diameter. Reproduces by seed and by rooting at nodes and will regenerated from plant fragments.

Impacts: Yellow floating heart grows
in dense patches, excluding light for native species and creating stagnant areas with low oxygen levels underneath the floating mats. These mats make it difficult to fish, water ski, swim or paddle. It displaces native plants and animals and decrease biological diversity. This troublesome aquatic changes how natural ecosystems work. Grows on slow-moving rivers, lakes, reservoirs, and ponds. 7

WATER HYACINTH
(Eichhornia crassipes (Mart.) Solms) Water hyacinth is native to South America, and was introduced to the United States in the 1880s. It’s beautiful, large purple and violet flowers have made it a popular ornamental, and the plant is now naturalized in most of the southern United States. Currently it is only known to occur in two Oregon counties, but doesn’t appear to be overwintering in either. Waters with thermal springs upstream, or cooling ponds for power plants (the case in a reoccurring infestation in WA) would be prime spots for infestations to persist.

Description: Water hyacinth has been called the worst aquatic plant in the world! Its
growth rate is among the highest of any plant known: hyacinth populations can double in as little as 12 days. The plant is a free-floating, robust plant that can grow up to three feet off the water's surface with a mass of fine purplish black and feathery roots hangs in the water underneath the plant. The shiny green leaves are round to oval, four to eight inches in diameter, with gently incurved sides. The leaf veins are dense and numerous, so leaves stand erect. Water hyacinth stalks are bulbous and spongy, and help keep the plant buoyant. The flowers have six petals, purplish blue or lavender with yellow. There are several flowers grow at the top of a single stalk. The plant reproduces by seeds and vegetatively through daughter plants that form on rhizomes and produce dense plant beds. In one study, two plants produced 1,200 daughter plants in four months. By this mechanism, water hyacinth can form impenetrable mats of floating vegetation. Individual plants break off the mat and can be dispersed by wind and water currents. A single plant can produce as many as 5,000 seeds and waterfowl eat and transport seeds to new locations. Seedlings are common on mud banks exposed by low water levels. Another tropical floating-leaved nursery plant, called water lettuce, may be mistaken for water hyacinth However; water lettuce doesn't have showy flowers and has large ribbed leaves. Water lettuce is much less cold-tolerant than water hyacinth and is not thought able to survive in cold climates

Impacts: Forms dense colonies that block sunlight, clog water intakes, and crowd out
native species. Incredibly dense mats of free-floating vegetation block boat traffic and prevent swimming and fishing, and keep sunlight from reaching the water column and submerged plants.

8

GIANT SALVINIA
(Salvinia molesta) Other Common Names: giant salvinia, Kariba weed, African pyle, aquarium watermoss, koi kandy

Salvinia molesta, one of the world’s most noxious aquatic weeds, is notorious for dominating slow moving or quiet freshwaters. Giant salvinia is native to South America.

Description: It is a small free-floating plant that grows in clusters and develops into
dense, floating mats or colonies in quiet water, undisturbed by wave action. The floating leaves of giant salvinia are oblong (0.5 to 1.5 inches long) with a distinct midrib along which the leaf may fold forming a compressed chain-like appearance. Salvinias have stiff leaf hairs on the upper surface of the leaves. In giant salvinia the leaf hairs have a single stalk that divides into four branches that reconnect at the tip, giving the hair a cage-like or egg-beater appearance. Underwater the leaves are modified into small root-like structures. The entire plant is only about 1 to 2 inch in depth. Salvinias are ferns and have no flower. Giant salvinia has sporangia but are thought to reproduce only by fragmentation. Giant salvinia can double in size in 4 to 10 days under good conditions. Giant salvinia is an aggressive invader species. Under optimal conditions (light, temperature and nutrient) in the laboratory, plant populations have been found to double in size every 2-4 days. Salvinias have no known direct food value to wildlife and is considered an exotic and highly undesirable species.

Impacts: Its rapid growth, vegetative reproduction and tolerance to environmental stress
make it an aggressive, competitive species known to impact aquatic environments, water use and local economies. These colonies will also eliminate native submerged plants by blocking sunlight penetration. Resulting dense surface cover prevents light and atmospheric oxygen from entering the water. Meanwhile, decomposing material drops to the bottom, greatly consuming dissolved oxygen needed by fish and other aquatic life. 9

YELLOW FLAG IRIS
(Iris pseudacorus) Other common names: Water Flag, Yellow Flag and Yellow Iris Yellow flag is native to most European countries with the exception of Iceland. It is also known to occur in North Africa and the Mediterranean regions. It has significant freeze tolerance and can be found in Scandinavia to 68 degrees North. Yellow flag iris is a popular ornamental in North America that is planted in natural and artificial wet areas within urban and rural landscapes. It is particularly popular as a large and colorful flowering element in ponds and has been planted in wastewater ponds where it is used to remove heavy metals. The species has naturalized extensively and is currently distributed across the United States. Once established, it is an aggressive invader in most wet habitats. In Oregon, significant populations can be found in the Willamette valley, in coastal lakes and streams, in the Columbia and Snake Rivers and in Central Oregon on irrigation canals. This plant is known to occur in two locations in Wallowa County and other small populations throughout northeast OR.

Description: Yellow flag is a very showy species growing
3-4 feet in height with the most vigorous growth attained in the wettest environments. The leaves are long, flattened and sword-like, typical of most iris. Large plant clumps are formed from the lateral growth of rhizomes sometimes attaining 20 feet in width. It has erect plant stalks with multiple flowers produced on each. Fruit capsules are large, 3-angled and up to 4 inches in length. Disk-like seeds are shed from the capsules throughout the fall and winter. Floating mats of seed can be observed in backwaters and marshes aiding dispersal. Reproduction can occur asexually through rhizome fragmentation or by seed production.

Impacts: An infestation of yellow flag iris presents a dual impact on both human interests
and native environments. This plant displaces native plants including sedges and rushes. This can reduce the carrying-capacity of wetlands for waterfowl and disrupt other ecological relationships. Irrigation canals and flood control ditches can be severely restricted by the physical nature of the plant clumps. Removal can be costly requiring large excavation equipment or herbicides. Control of heavily infested waterways can be cost prohibitive due to the huge volume of plant material needing to be removed. Any rhizome fragments that remain quickly reestablish a population. Many over-wintering waterfowl species are dependent on sedge and rush seeds as a high-energy food source. Replacement of this food source with yellow flag iris would reduce the carrying capacity of these marshes to sustain waterfowl populations. A small volume of yellow flag still exists in the nursery trade. A variegated variety is popular with aquatic gardeners and can be found in several catalogs and web sites. 10

EUROPEAN WATER CHESTNUT
(Trapa natans L) Other common names: Singhara Ling, bullnut Little information is available as to how this plant got established in the United States. It is most likely that T. natrans was brought from Europe as an ornamental. Currently, there are no known populations established in the state of Oregon.

Leslie J. Mehrhoff, University of Connecticut

Description: Annual aquatic plant. Upper
floating leaves diamond-shaped with toothed Leslie J. Mehrhoff, edges, arranged on inflated, spongy stalks and University of Connecticut occur in clusters up to 20 inches across. Submersed leaves long and narrow or often replaced with green feather-like structures. Flowers small, solitary and white to light purple. Fruit a large swollen nut with two to four sharp spines.

Impacts: This plant is a fierce competitor in shallow
bodies of water possessing soft, muddy rooting substrates. In the Northeast it creates nearly impenetrable mats across wide areas of water creating barriers to boaters, swimmers and fisherman alike. Spiked nuts drift to shore where their sharp spines may hurt bare feet. Mono-cultures severely limit light penetration and water mixing, creating conditions of reduced oxygen levels which may increase the potential for fish kills. It is of little value to waterfowl.

Alfred Cofrancesco, U.S. Army Corps of Engineers

11

EUROPEAN FROGBIT
(Hydrocharis morsus-ranae L.) This plant occurs around the Great Lakes and is only found in New York State within the United States. It is found in Ontario and Quebec in Canada. Frogbit is currently on the Washington State’s noxious weed list.

Description: Plants perennial, of fresh waters.
Rhizomes absent; stolons present. Stems floating on or suspended in water, rooted or not, unbranched, short. Leaves basal, emergent or floating, petiolate; blade cordate to reniform or orbiculate, base reniform or cordate, apex obtuse to almost truncate; midvein without rows of lacunae along sides, uniform in color throughout, abaxial surface without prickles, smooth on emergent leaves or with aerenchymous tissue on floating leaves; intravaginal squamules entire. Inflorescences 1-flowered or cymose, sessile or short-pedunculate; spathe not winged. Flowers unisexual, staminate and pistillate on different plants [on same plants], emersed, pedicellate; petals white to pinkish. Staminate flowers: filaments distinct or basally connate, distinct portion longer than connate; anthers oval; pollen in monads. Pistillate flowers: ovary 1-locular; styles 6, 2-fid less than ½ length. Fruits spheric, smooth to ridged, dehiscing irregularly. Seeds ellipsoid, minutely tuberculate or muricate.

Impacts: The impacts associated with this
weed are very similar to other aquatic invasive species. It forms dense mats that eliminate native species and creates conditions of reduced oxygen levels which may increase the potential for fish kills.

12

CAROLINA FANWORT
(Cabomba caroliniana)

Fanwort is a native of the southeastern U.S, but is considered to be a non-native invasive plant in the northeastern U.S. and in the northwest. The plant is known to be present in Columbia, Clatsop, Lane and Douglas Counties in Oregon. Two species of Cabomba occur in Florida.

Description: Fanwort is a rooted submersed plant. It may have
submersed and floating leaves of different shapes. Fanwort generally grows in three to ten feet of water, and is found in ponds, lakes and quiet streams. Fanwort stems are long and much-branched. Fanwort has fan-like underwater leaves, which are about two inches across. The submersed leaves are frequently divided, and are arranged oppositely or in whorls along the stem. The floating leaves are small, diamond-shaped, and are infrequent. Fanwort flowers are white to pink to purplish and are about 1/2 inch across. The flowers are on stalks which arise from the tips of the stems.

Impacts: Although the potential impacts are not clear at
this time, it is believed that they would be similar to other aquatic invasive plant species. By forming dense mats, this plant out-competes native species and reduces the overall ecological diversity. 13

FEATHERED MOSQUITOFERN
(Azolla pinnata R. Br.) Other common names: Feathered Mosquitofern, Mosquito Fern or Water Velvet

Azolla pinnata can spread rapidly, and has the ability to survive on moist soil in and around rivers , ditches, and ponds . Azolla is usually found in stagnant or slow-moving water of ponds, lakes, marshes, swamps, and streams. Plants turn reddish when under stress, such as from poor nutrition, salinity, or high temperatures. A. pinnata has been cultivated for many centuries in rice paddies of northern Vietnam and southeastern China, where it acts as a fertilizer after it decomposes.

Description: Plants small, 1.5 - 2.5 cm long, with a
straight main axis with pinnately arranged side branches, progressively longer towards the base , thus roughly triangular in shape. The basal branches themselves become pinnate and eventually fragmenting as the main axis decomposes to form new plants. Roots with fine lateral rootlets, having a feathery appearance in the water. Leaves minute, 1 -2 mm long, overlapping in 2 ranks , upper lobe green, brown green or reddish, lower lobe translucent brown; minute, short, plae, +/cylindrical unicellular hairs often present on the upper lobes. When fertile, round sporocarps 1 - 1.5 mm wide can be seen on the under-side at the bases of the side branches. The leaves often have a maroon-red tinge and the water can appear to be covered by red velvet from the distance. The upper surfaces of the leaves are totally water-repellant, and if completely submerged the plants quickly refloat with the right side up.

Impacts: It forms dense surface mats, which degrade water quality by reducing oxygen
levels, and can interfere with boating, fishing and recreational activities.

14

PARROT FEATHER WATERMILFOIL
(Myriophyllum aquaticum) Other common names: Brazilian Water-Milfoil, Brazilian Watermilfoil, Parrot Feather, Parrot Feather
Watermilfoil, Parrot´s-Feather, Parrot's Feather, Parrot's-Feather, Parrot-Feather, Parrotfeather, Parrotfeather Water Milfoil, Parrotweed, Thread-Of-Life, Water Milfoil, Water-Feather

M. aquaticum is a bright or glaucus green perennial freshwater herb. Parrots feather exhibits two different leaf forms depending on whether it is growing as a submerged plant or as an emergent. It is found in freshwater lakes, ponds, streams, and canals and appears to be adapted to high nutrient environments, and does well in good light and a slightly alkaline environment. Almost all plants are female, and male plants are unknown outside of South America. It has been introduced for use in indoor and outdoor aquaria and is also a popular aquatic garden plant. It tends to colonize slowly moving or still water rather than in areas with higher flow rates. While it grows best when rooted in shallow water, it has been known to occur as a floating plant in the deep water of nutrient-enriched lakes. The emergent stems can survive on wet banks of rivers and lake shores, so it is well adapted to moderate water level fluctuations.

Description: Herbs perennial, rarely annual, aquatic or
terrestrial, monoecious or dioecious. Stem creeping, ascending or erect, often rooting at lower nodes. Leaves estipulate, 2-4-whorled, decussate, or alternate, in terrestrial species always simple, in aquatic submersed species always pectinately lobed. Inflorescence an indeterminate or determinate spike of 1-5-flowered dichasia borne in axils of leaflike primary bracts. Flowers minute, actinomorphic , epigynous , protandrous, anemophilous or entomophilous, bisexual or unisexual. Stamens 1 or 2 Ã as many as sepals; filaments short, slender; anthers basifixed , mostly oblong or linear , 4-loculed, dehiscing by slits, antisepalous anthers sometimes somewhat longer than antipetalous ones; styles as many (rarely half as many) as sepals, alternisepalous, free , mostly short, grading into globose or subulate stigmas, spreading in fruit; stigmatic papillae hairlike; ovules as many as styles, rarely 1, apical, pendulous, anatropous . Fruit nutlike or a drupe, variously ornamented with wings, ribs, and tubercles, indehiscent and 1-seeded or breaking up into (2-4) 1-seeded mericarps; Seeds with thin testa; embryo cylindric, surrounded by thick, white albumen.

Impacts: It has escaped cultivation and spread via plant fragments and intentional
plantings. It forms dense surface mats, which degrade water quality by reducing oxygen levels, and can interfere with boating, fishing and recreational activities. 15

TWOLEAF WATERMILFOIL
(Myriophyllum heterophyllum Michx.) Other common names: Variable milfoil It was most likely a “stowaway” fragment attached to a boat or trailer that came to the northeastern US region. Milfoil can live out of water for many hours if it remains moist, like when it’s wound around a wet carpeted bunk on a boat trailer or in a live well. Milfoil is usually first found near boat launch sites when it infests a new waterbody, a sure sign that transient boaters are the leading means of spread. Another theory is that milfoil was introduced to a New Hampshire waterbody through the dumping of a home aquarium. The plant is new to the Pacific Northwest, but commonly used as ornamental plant in fish aquariums.

Description: Milfoil is a submerged aquatic plant
with fine densely packed, featherlike leaves whorled around a main stem. It can grow up to 15 feet and may exhibit a three to six inch green spikelike flower above the waterline in late June or in July. A crosssection of the stem will reveal “pieshaped” air chambers. Boat propellers chop These fragments of the wind and lake these fragments. If take hold creating a until every suitable alternative form of This vegetation type form and can persist milfoil plants into small fragments. float on the surface and are at the mercy currents. In a short time, roots form on washed ashore, these plants eventually new colony of milfoil. The cycle goes on area is filled in with these weeds. An the plants develops during low water. is more succulent than the submersed for moderate periods of low water.

Impacts: This species is not native to our state and is very difficult to control once it
becomes fully established. Milfoil reproduces through fragmentation whereby plant fragments break off from the parent plant through wind or boat action, grow roots, and settle in a new location. Seeds are also a means of spread within an infested waterbody. Milfoil spreads rapidly and displaces beneficial native plant life, often forming monoculture of growth around the shallows of a waterbody. It makes swimming difficult and can devalue waterfront property. Where this species grows in its native environment, insects and fish may feed on this plant at such a rate as to control its growth. In New Hampshire, variable milfoil has no abundance of natural predators to keep its population in check. Under optimum temperature, light and nutrient conditions, milfoil may grow up to an inch per day. 16

WHITE WATERCRESS
(Rorippa nasturtium-aquaticum syn. Nasturtium nasturtium-aquaticum, Nasturtium officinale, Sisymbrium nasturtium-aquaticum) White watercress is native to Europe. The plant grows in lakes, ponds, rivers, streams, springs and moist ground.

Description: Alternate, nearly toothless,
pinnately lobed with 3 to 9 leaflets. The terminal leaflet is larger than the side ones. Leaflets oval shaped.

Flowers: White, small, 0.2 inches wide, 4
petalled flowers borne on long stems, appearing April through September.

Fruit: Slender pods are about 0.4 to 0.6
inches long. The seeds within the pod are small and are contained in two rows.

Look-alikes: Onerow yellowcress
(Rorippa microphylla), a non-native, is very difficult to distinguish from white watercress in the field. They both occur in moist soils and behave similarly. Onerow yellowcress seed appear in one row in the pod and a slightly larger and more prolific than white watercress seeds.

Impacts: White watercress rapidly forms
dense stands that exclude native plants. White watercress is uncommon but spreading rapidly. It is highly threatening to natural plant communities. All detected occurrences should be eradicated. 17

NARROWLEAF CATTAIL
(Typha angustifolia) Other common names: Cattail, Narrow-leaved Cattail, and in the UK, Bulrush, Lesser Bulrush, Small Reed Mace Narrow-leaved cattails are believed to have been introduced to the Atlantic seaboard from the dry ballast of European ships. This plant has since spread westward and occurs throughout much of the United States, and is found in southeast OR. The hybrid cattail is concentrated in the northeast, but may occur wherever both the native and the narrow-leaved species are present. It is found in wetlands, ditches, stream and lake shores and wet depressions; tolerates high levels of silt, nutrients and salt. Typha angustifolia hybridizes with the native common cat-tail (Typha latifolia) to produce Typha X glauca. The hybrid cat-tail is larger than parents, sterile; reproduces vegetatively through rhizomes; tolerates a greater range of conditions than parents.
Photo: Ohio Department of Natural Resources, Division of Natural Areas and Preserves, http://www.dnr.state.oh.us/dnap/invasive/11cattail.htm

Description: An erect, rhizomatous, semiaquatic or aquatic, perennial herb. The leaves
are erect, linear, flat, basal, very narrow and flattened (¼"-½" wide and 3'-6' tall). Twelvesixteen leaves arise from each vegetative shoot. The stems are stout and erect (3-6 feet). Rhizomes are stout, produced at the leafbase and up to 27 inches long; typically ¾"-1½" in diameter. The flower structure is a dense, fuzzy, cylindrical spike on the end of stem, with a distinct gap of 1"-3" of naked stem between the upper, male portion (staminate) and the lower, female (pistillate) portion. Both male and female sections are roughly the same length. Male flowers are lighter brown; female flowers often green during bloom turning dark brown during seed maturation. Individual blossoms are minute and closely packed on spike, blooming May-June. The fruits are cigar-shaped and 2"-6" long, with soft, downy seeds. Seeds of Thinleaf cattail are a tiny nutlet, about 1 mm long with downy hairs underneath Seeds remain viable in the seed bank for up to 100 years.

Impacts: Narrow-leaved and hybrid cattail will outcompete native plants in wetland systems. These plants establish dense monocultures that enable them to shade out native vegetation. They are also thought to be allelopathic, producing chemicals which discourage growth of other plant species. Cattails reproduce both vegetatively by rhizomes and sexually through massive amounts of seed. 18