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River-Lab 5 Guide Manual
Invasive Plant Information
Phragmites (Phragmites australis)
Appearance and general information:
 Flower plumes at the top of the stem produce 1000s of seeds dispersed by
wind and water.
 Long, flat, slender leaves
 Grows 5 to 15 feet tall
 Grows in fresh and brackish water (mix of salt and fresh) but grows best in low
levels of salinity
 Tolerates a wide range of conditions: from dry to flooded
Invasive qualities:
 Reproduces aggressively through the spread of rhizomes (underground stem
system) up to 10 feet horizontally a year under good conditions
 Rhizomes (stems that grow horizontally at or above soil level) can grow to a
length of 17 to 34 feet.
 The rhizomes can break off and spread with water currents creating more
stands of Phragmites in other areas.
 Dense growth pattern (200 stems per square meter) creates a monoculture*
which shades other species preventing their growth
 Not many animals eat it
Why it out-competes native species:
 Dense growth pattern creates monoculture*; reduces diversity of native plants
 Reproduces aggressively
 Lack of a native organism(s) to eat or control growth
 Reduces habitat space for native plant species
Japanese Knotweed (Polygonum cuspidatum)
Appearance and general information:
 Stalks sprout in early spring: green with red flecks, thick as a finger.
 Mature plants grow to heights of over 10 feet.
 Leaves are green, large, and heart-shaped.
 Flowers are clusters of small white flowers.
 Grows in dense clumps
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© 2009 Mill River Wetland Committee, Inc.
River-Lab 5 Guide Manual
Invasive qualities:
 Develops an extensive network of underground stems called rhizomes that can
sprout many new plants.
 Can also spread to new locations: flood waters move pieces of stem and
rhizomes downstream where they can start new plants
 Shades the ground under itself, which reduces the amount of sunlight so the
smaller native plants can’t grow
 It can reproduce easily because it produces so many seeds and the rhizomes
sprout new plants every few inches.
Why it out-competes native species:
 Dense growth pattern creates monoculture*; reduces diversity of native plants
 Reproduces aggressively
 Lack of a native organism(s) to eat or control growth
 Reduces habitat space for native plant species
Japanese Stilt Grass (Microstegium vimineum)
Appearance and general information:
 Plant has branched stems that spread out over the ground
 Mature plants grow 1 to 3 feet in length
 Pale, green lance-shaped leaves (sword-like)
 Leaves are 1 to 3 inches long.
 Leaves have distinctive shiny midrib.
 Flower spikes with tiny greenish-white flowers are produced in late summer
 Each plant may produce up to 1000 seeds.
 Grows in a variety of conditions and locations (open areas to shady, moist to
dry soils) and is highly adapted to growing in low light conditions.
Invasive qualities:
 Seeds can be carried by water currents.
 Seeds may also be carried by foot traffic by animals and humans.
 Seeds remain viable for 5 years after plant dies back.
 Plants spread to form extensive patches, displacing native species.
 Deer feed on native grasses and avoid stilt weed, helping to facilitate invasion.
 New plants can be produced when stems touch soil: roots can sprout from
stem-to-stem junctions and stem-to-leaf junctions.
© 2009 Mill River Wetland Committee, Inc.
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River-Lab 5 Guide Manual
Dies back each fall after spreading its root system.
 Shades out native plants that need sunlight.
 Changes soil chemistry so native plants cannot grow.
Why it out-competes native species:
 Dense growth pattern creates monoculture*; reduces diversity of native plants
 Reproduces aggressively
 Lack of a native organism to eat or control growth
 Changes soil chemistry preventing growth of native plants
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Oriental bittersweet (Celastrus orbiculatus)
Appearance and general information:
 Woody stemmed climbing vine
 Dark green, oval leaves
 Orange roots
 Red fruit/berries with yellow petal-like outer covering
Invasive qualities:
 Produces more berries than the native bittersweet
 Berries contain more seeds than the native bittersweet
 Seeds have a higher rate of germination
 Brighter red berries attract more birds.
 Also spreads by roots and rhizomes that send up new shoots farther away from
the original plant.
 Interbreeds (hybridizes) with native species
 Strangles and smothers surrounding vegetation
 Better at photosynthesis than native: it absorbs light from a wider range of the
spectrum
Why it out-competes native species:
 More attractive to birds than native bittersweet which accelerates its spread
(seeds from bird wastes sprout new plants)
 Produces more seeds with a higher rate of germination
 Reproduces aggressively through the spread of seeds and root suckering
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© 2009 Mill River Wetland Committee, Inc.
River-Lab 5 Guide Manual
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Interbreeds with the native species
Strangles surrounding vegetation
Multi-flora Rose (Rosa Multiflora)
Appearance and general information:
 Thorny arching stems
 Stems covered with downward pointing soft thorns (prickles).
 Can grow to 15 feet high and wide
 Leaves divided into 5-11 sharply-toothed leaflets
 Fragrant white flowers clusters appear in May and June, continuing throughout
growing season
 Each panicle (flower cluster) of 40-50 flowers produces a bright red fruit (rose
hip) during the summer, which remains on plant through the winter.
 Each hip can have as many as 17,500 seeds; therefore one plant can produce 1
million seeds.
Invasive qualities:
 Hips are eaten by birds and small mammals, dispersing seeds through wastes
 Seeds can remain viable in the soil and are able to germinate for 10-20 years.
 Stems can root when they come in contact with soil (layering), forming
impenetrable thickets.
 Fibrous roots can produce new roots and plants.
Why it out-competes native species:
 Dense growth pattern creates monoculture*; reduces diversity of native plants
 Forms impenetrable thickets which reduces sunlight and nutrients for native
plants
 Reduces habitat space for native plant species
 Prolific seed reproduction and aggressive growth (seeds and layering) make it
difficult for native plant species to grow
 Lack of a native organism(s) to eat or control growth
*monoculture-- the only plant growing in a particular area that leads to a lack of
diversity
© 2009 Mill River Wetland Committee, Inc.
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