Invasive species are among the biggest threats to our local ecosystems, posing serious risks to native wildlife and plants. These species, often introduced accidentally, thrive without natural predators, leading to the destruction and displacement of native species and their habitats.
General Traits of Invasive Plants
Many plants in an area may be non-native, but only a few become invasive. To be considered invasive, plants typically:
- Grow rapidly and adapt easily
- Cause economic or property damage
- Harm native plants
- Reproduce quickly, often producing many seeds that spread easily
Other common traits of invasive plants include:
- Ability to reproduce in multiple ways (e.g., through root cuttings, rhizomes, dropped leaves, seeds, self-fertilization)
- High tolerance to disturbances
- Vigorous root systems
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REGIONAL INVASIve species guide
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Invasive Species - Species of Concern
DSV Pods at Turnbull Ranch Nature Reserve taken by Danielle Houston
Dog-strangling Vine (Vincetoxicum rossicum & Vincetoxicum nigrum)
Dog-strangling Vine is an invasive climbing vine from Eurasia that crowds out native plants and harms Monarch Butterflies. It was introduced to Canada as an ornamental plant.
Identification:
- Grows 1 to 2 meters tall, twining around plants or structures.
- Oval leaves (7 to 12 cm) grow in pairs opposite each other.
- Small, star-shaped flowers are pink to purple.
- Bean-shaped seed pods (4 to 7 cm) release feathery seeds in late summer.
Phragmites at Wilsons Point Wetland taken by Megan Greenwood
Invasive Phragmites Reed (Phragmites australis australis)
Invasive Phragmites, a tall perennial grass from Eurasia, threatens wetlands by taking over water and nutrients, crowding out native plants, and releasing toxins from its roots. It can grow in both wet and dry areas, forming dense stands that reach up to 5 meters tall. Identifying it can be tricky since it resembles native reeds, but invasive Phragmites stands out with tan stems, blue-green leaves, and large, dense seed heads.
Garlic Mustard plant with first-year foliage. taken by Aiesha Aggarwal
Garlic Mustard, native to Europe, was introduced to North America in the 1800s as an edible herb. It’s now an invasive species that thrives in forest understories, outcompeting native plants. Its seeds can survive in the soil for up to 5 years, making it hard to eliminate.
Identification:
- Leaves emit a strong garlic odor when crushed.
- First-year plants form a rosette of dark green, kidney-shaped leaves (up to 10 cm across).
- Second-year plants grow stems up to 1.2 m tall with triangular, toothed leaves arranged alternately.
- Blooms in May with small, white, four-petaled flowers.
- Produces narrow seed pods (2.5 to 6 cm) that release tiny black seeds in mid-summer.
Purple Loosestrife taken by Invasive Species Centre
Purple Loosestrife (Lythrum salicaria)
Purple Loosestrife invades wetland habitats, adding excess nutrients to the water and causing eutrophication, which lowers biodiversity and disrupts ecosystems. It can also reduce water levels and outcompete native plants.
Identification:
- Grows 60-120 cm tall with 1-15 square stems.
- Stems may be branched with fine, smooth hairs.
- Lance-shaped leaves (3-12 cm long) have smooth edges and turn bright red in autumn.
- Deep pink to purple flowers bloom from June to October.
- Tiny, round seeds are found in small capsules (3-6 mm long)
Common Buckthorn taken by Invasive Species Centre
Common & Glossy Buckthorn (Rhamnus cathartica & Frangula alnus)
Common and Glossy Buckthorn, shrubs from Eurasia, were introduced to Canada in the 1800s as ornamental plants and for agricultural use. Now invasive in Ontario, they form dense stands that outcompete native plants and alter soil quality.
Common Buckthorn:
- Leaves emerge early in spring and persist until late fall.
- Grows in dry areas, often reaching 3 meters tall.
- Twigs and branches end in a single, short thorn.
- Smooth, dark green leaves with fine teeth, arranged in pairs along the stem (2.5 to 6 cm long).
- Produces clusters of black, berry-like fruit in late summer and fall.
Scots Pine taken by Toby Rowland
Scots pine, introduced to Ontario from Europe in the early 1900s to address soil erosion on abandoned agricultural lands, is now widely naturalized. However, it has invasive tendencies. Its vulnerability to pests and diseases can result in the spread of harmful insects and pathogens to native trees, creating challenges for management and conservation efforts.
Identification:
- Grows up to 35 meters tall and 1 meter wide.
- Often crooked trunk with sparse branches and an uneven top.
- Lower Trunk bark: Thick, dark grey-brown. Upper Trunk and Branches: Thin, orange-brown.
- Mature Tree needles: Dull grey-green, 2.5-5 cm long, in pairs. Young Trees: Longer, sometimes in groups of three or four.
- Male Cones: Yellow or pink, 8-12 mm long. Female Cones: Start small and round, become larger and pointed over 2-3 years.
- Seeds: Black, 3-5 mm long, with a tan wing 12-20 mm long.
- Roots: Usually shallow but can develop a deeper root in dry soils.