top of page

Invasive Species

What Is An Invasive Species?

An invasive species is a non-native species which successfully reproduces and thrives in their new environment while outcompeting native species.

Below are descriptions of the invasive species we find within our watershed, click on each picture for more in depth information on each species.

Invasive Plants in Our Watershed

Glossy Buckthorn

  • Introduced from Europe as an ornamental shrub

  • It is an aggressive invasive with white-speckled brown branches, grows up to 20 feet

  • Alternate shiny oval leaves with smooth edges

  • small white star-shaped flowers bloom in June, these are replaced by red berries which turn black when mature

  • Mostly spreads from birds carrying their seeds after eating its berries

Japanese Knotweed

  • Originally brought to North America from Japan as an ornamental shrub

  • A semi-woody, green shrub with hollow insides that can grow up to 8ft tall

  • Alternate round to heart-shaped leaves grow from swollen nodes along the main stem

  • Clusters of small creamy white flowers bloom between August and September

  • Mostly spreads from fragments of its root rhizomes moving to new places but can easily propagate from stem transfers

Bittersweet Nightshade

Bittersweet nightshade in taking over stream_3233.JPG
  • Introduced to North America from Europe/Asia for ornamental and medicinal uses

  • Perennial climbing vine which forms dense clusters and steams which start out herbaceous turning woody when mature

  • Heart shaped alternate leaves

  • Small star-shaped Blue-violet flowers bloom between May and September, these are replaced by green berries which turn red when mature

  • Mostly spread from birds eating berries but pieces of stem and root carried by water/soil can start new colonies

Common Valerian

Screenshot 2024-02-09 142001.png
  • Native to Eurasia, it was brought to North America as an ornamental/medicinal plant

  • 1.5-5ft tall when mature with thick, fleshy, ridges stems

  • compound, pinnately divided leaves with 5-25 leaflets/leaf with small serrated edges and fuzzy undersides

  • White-pink dense flowers cluster into an umbrella-like shape with a strong fragrant smell, blooms from June to August

  • Spread vigorously by self seeding and aerial stolons.

Black Knapweed

20231010_135537 black knapweed.jpg
  • Native to the Mediterranean but naturalized across Europe. Brought to North America as an ornamental Species.

  • first year the plant is in a rosette near the ground, second year plants produce narrow, long, hairy stems 30-150cm in height.

  • Leaves on lower portion are lance-shaped and 5-25cm long ,as they move up the stem their size decreases.

  • Flowers occur at terminal end of stalk with purple top and green bulbous shape below 

  • Creates many seeds/flower head that spread easily

Purple Loosestrife

  • Native to Eurasia, how it got to North America is unclear but may have been ship ballast or ornamental typically 

  • 0.5-1.5m tall when mature

  • Leaves usually opposite and paired but can be alternate and come up in whorls of three.

  • small lane-shaped leaves

  • Bloom July-September with purple-pink flowers attached closely to the stem.

  • Spread easily via the numerous seeds produced by the fruit.

Common Mullein

2023-08-02 Common-Mullein-Potential-Invasive IMG_7843.JPG
  • Comes from Europe/Asia and was brought to North America for medicinal/herbicidal use

  • In its first year, the plant remains near the ground in rosettes, second year its thick stalk can grow 1-2m in height. 

  • First year leaves small oblong-elongated in rosette, mature leaves are elongated and wooly, arranged alternately around the stalk. 

  • Flowers grow in an 20-50cm long spike with numerous five-petaled yellow flowers, brown seed pods replace flowers each containing thousands of tiny red seeds.

  • Spreads through seed and taproots.


Screenshot 2024-02-09 144045.png
  • Comes from Europe/Asia originally but spread throughout most other continents.

  • commonly found in cold, alkaline spring water

  • Alternate, pinnately-compound leaves

  • Flowers from March to October with small four-petaled white flowers

Multiflora Rose

  • Originally from Asia, brought to North America as root stock for ornamental roses and later promoted as a barrier to erosion.

  • Medium sized thorny shrub growing up to 5m tall, branches (canes) form large arches and when they touch the ground they form new roots. 

  • Leaves are divided into 5-11 toothed leaflets.

  • Flat clusters of small white to pink flowers bloom between May and June, bright red rose hips form after flowering. 

  • Spread by seeds and stem propagation 

Invasive Animals That Threaten Our Watershed


Photo by Rosie McFarlane
  • Originate from Asia, brought to North America as an aquarium pet/ornamental species

  • Named for their golden appearance, these fish typically appear orange but can range in colour from white to black to spotted.

  • Goldfish grow to be between 5 and 25 inches and live up to 30 years under ideal conditions.

  • Goldfish eat algae, plants, invertebrates and fish eggs. While feeding they disturb the bottom of the water causing particles to enter the water column. This increases turbidity blocking light from aquatic plants.

  • While not strong competitors, their disruption of the ecosystem causes them to be one of the most problematic invasive species.

Green Crab

Source: Government of Canada, DFO

Rainbow Trout

  • Originates from Europe, they are believed to have come to North America through ship ballasts. 

  • up to 10cm carapace width, typically have a yellow-green coloured shell but can be red/orange. Carapace has deeply toothed edges near the face. They also have two different sized claws.

  • Green crabs are voracious and destructive species, consuming anything they can. They are an aggressive species that is known to destroy sea grass beds, damaging shorelines.

  • Green crabs reproduce rapidly, adult females can release up to 185 000 eggs twice a year.

PEI Invasive Species Council's Don't Move Firewood Campaign

I an effort to reduce this risk of certain invasive species entering/spreading through PEI, the invasive species council set up a program to regulate transport of firewood. Species such as the Asian Long-Horned Beetle and the Brown Spruce Longhorn Beetle are often transported through firewood, so with the cooperation of local campgrounds, the PEIISC has successfully placed restrictions on the movement of firewood. 

Asian Long-Horned Beetle

ALHB. Photo by Kenneth R. Law, USDA APHIS PPQ,

Brown Spruce Longhorn Beetle

Brown spruce longhorn beetle. Photo by Georgette Smith, Canadian Forest Service,
bottom of page