The dog-strangling vine — along with having an unpleasant name — is responsible in part to the decline of monarch butterflies.

The vine has made a new top 10 list: this one warning of the most invasive and destructive plants in Canada.

"Monarch butterflies can sometimes mistake it for milkweed, but when they lay their eggs on it, the caterpillars can't develop into butterflies and they die," said Dan Kraus, a senior conservation biologist with the Nature Conservancy of Canada.

NCC released the list Friday to bring attention to the plants, some of which are still sold in garden centres, with the hopes people will spot them and report them.

In the case of the dog-strangling vine, it grows quickly, often over other plants preventing the native plant from growing and getting sunlight. In some areas of the country, you can find fields of it, Kraus said.

Toronto Japanese knotweed

It might be pretty, but Japanese knotweed has been identified by the International Union for the Conservation of Nature as one of the world’s worst invading species. (John Rieti/CBC)

Threatens insects, songbirds

The impact of the plants goes beyond just harming native plants. Common tansy produces a toxic compound that impacts cattle and wildlife.

The others, like dog-strangling vine, affect insects.

"[The invasive plants] just don't support the numbers and diversity of our native insects, and that has an impact on songbirds," he said.

"Once they get into a natural environment, they're able to continue to spread on their own and they have an impact on our native plants and our native animals." 

Hospitality concerns

One of the reasons these plants are spreading? People.

"We tend to find more invasive plants in habitats that are fragmented or impacted by people," Kraus said.

Climate change may also be making Canada more hospitable to invasive plants.

"We're concerned with warming temperatures, we may have more and more plants that are starting to take hold and are able to spread into our natural environment," he said.

There are two things Kraus would like to see people do. The first it to learn about the plants on their own property "that have a track record of escaping into natural areas." That includes purple loosestrife and Japanese knotweed.

The second is be a spotter and report sightings of the plants.

"One of the exciting things about conservation right now is that we can all play this important role in reporting invasive plants," he said.

Using apps like iNaturalist and EDmaps can alert scientists and land managers to the invasive species so they can take action.    

Canada Thistle

Canada thistle crowds out native plants. (Scott Neufeld/CBC)


Top 10 invasive plants in Canada

Nature Conservancy 2017 list:

Knapweeds

There are five invasive knapweed species with slender stems and purple or white flowers. The plants were all unintentionally introduced from Europe in the late 1800s. It likely came over in alfalfa and clover seeds. Spotted knapweed is aggressive and is especially problematic in native grasslands in western Canada, and has recently spread to Manitoba.

Where it's found: Yukon, B.C., Alberta, Saskatchewan, Manitoba, Ontario, Quebec, New Brunswick, Nova Scotia.

Leafy spurge

This plant has yellow-greenish flowers and the leaves and stems have a white, milky sap. It probably came to Canada in grain seeds from Europe. It spreads quickly in open habitats and threatens habitats, such as tall grass prairie in Manitoba. In Saskatchewan, beetles have been introduced to the area as a biological control.

Where it's found: Yukon, BC, Alberta, Saskatchewan, Manitoba, Ontario, Quebec, New Brunswick, Nova Scotia, P.E.I.

Canada thistle/creeping thistle

This thistle is known for its purple flowers and spiny leaves. It has been established in North America for hundreds of years, although is not originally from Canada (despite the name). It crowds out native plants and reduces the quality of rangelands. Its small seeds also spread quickly in the wind.

Where it's found: Yukon, B.C., Alberta, Saskatchewan, Manitoba, Ontario, Quebec, New Brunswick, Nova Scotia, P.E.I.

European common reed

A tall reed with a bushy end, this plant has spread rapidly in eastern Canada, including in wetlands, along beaches and lakeshores. It has also spread quickly along roads and highways and the plant shades out native vegetation. The NCC has had a successful control project on Pelee Island in Ontario.

Where it's found: Alberta, Saskatchewan, Manitoba, Ontario, Quebec, New Brunswick, Nova Scotia, P.E.I., Newfoundland and Labrador.

Japanese knotweed

It resembles bamboo and was likely introduced as a garden plant, but the Japanese knotweed can form dense thickets and outcompete native vegetation. It's particularly a problem in Atlantic Canada where it takes over the edge of creeks and lakes. This one's a really bad one: It's been identified by the International Union for the Conservation of Nature as one of the world's worst invading species.

Where it's found: B.C., Alberta, Ontario, Manitoba, Ontario, Quebec, New Brunswick, Nova Scotia, P.E.I., Newfoundland and Labrador.

Garlic mustard

Garlic mustard is an invasive plant that also happens to be tasty. You can substitute it for basil to make a fresh pesto, for example. (Jonathan Pinto/CBC)

Garlic mustard

Native to Europe, this green-leafed herb with white flowers was first recorded in New York in 1868 and may have been brought over as a medicinal plant. It spreads through forests and displaces native species. Each plant produces thousands of tiny, black seeds that are viable in soil for many years. The only bright spot: The leaves can be picked and turned into a tasty pesto.

Where it's found: B.C., Alberta, Ontario, Quebec, New Brunswick, Nova Scotia, P.E.I.

Buckthorn

There are two kinds of this shrub — glossy false and European — which have berry-like fruits that produce large number of seeds. They were introduced in the late 1800s as an ornamental way to create windbreaks along farm fields, but the plant spreads quickly and prevents native trees and shrubs from regenerating. The common buckthorn is also the primary host for the non-native soybean aphid, a serious threat to farmers.

Where it's found: Alberta (European only), Saskatchewan (European only), Manitoba, Ontario, Quebec, New Brunswick, Nova Scotia, P.E.I.

Common tansy

With yellow, button-like flowers, this plant can grow as tall as 1.5 metres. It was introduced to North America from Europe in the 1600s as a horticultural and medicinal plant. It impacts stream banks and native grasslands and outcompetes native plants. It also produces a toxic compound that can impact cattle and wildlife.

Where it's found: Everywhere except Nunavut

European swallow-wort/dog-strangling vine

This vine can grow up to two metres long and takes over dense thickets or grows on other plants. Monarch butterflies have been known to lay eggs on the plant, but the larvae do not survive. The plant invades forests, stream banks, grasslands and alvar habitats (limestone plain). There is a moth from the Ukraine that lives on the vine, which has been been approved for release in North America.

Where it's found: B.C., Ontario, Quebec

Purple loosestrife

This plant from Europe is actually still sold in some places as an ornamental plant, but before adding it to your garden, you should know it crowds out most native vegetation and create near-monocultures. It has also by the International Union for the Conservation of Nature as one of the world's worst invading species because a single purple loosestrife plant can produce over two million seeds each year.

Where it's found: B.C., Alberta, Saskatchewan, Manitoba, Ontario, Quebec, New Brunswick, Nova Scotia, P.E.I., Newfoundland and Labrador.