Terrestrial Exotics, Aggressive Exotics, and Really, Really Nasty Exotics

This summer I have spent a fair bit of time hiking along a decommissioned railroad corridor. One previous post had described some of the flora while another one described some of the fauna. However as is typical with a lot of 'natural' areas in southwestern Ontario and elsewhere, there is a fair bit of non-native flora and fauna present. Some are colourful, some not so colourful, some are fairly benign while others are highly invasive. I'll leave the nastiest one of all that I have encountered, to the last of this post.

This post deals primarily with some of the lesser known, but problematic non-native species in a terrestrial environment. Others, especially some that are more well known and problematic in wetland environments will be discussed in a future post.

One of the less problematic terrestrial ones is Moth Mullein (Verbascum blattaria). It is not common anywhere that I have seen it here in southwestern Ontario, and is rather attractive.

Moth Mullein

Closely related to this is one that is probably more familiar to most readers: Common Mullein (Verbascum thapsus). It is definitely more problematic in woodland edges and disturbed sites.

Common Mullein

Many of the non-native species are very problematic in all sorts of areas where they can gain a foot-hold. They are early colonizing species, meaning they favour disturbed areas....and there is no shortage of disturbed areas in this part of the world!

Multiflora Rose (Rosa multiflora) is common place, even in prime natural areas such as Rondeau Provincial Park where it has come to dominate certain areas.

Multiflora Rose

Globe Thistle (Echinops sphaerocephalus) starts off looking a bit like a more common thistle, but soon appears with its characteristic globe shaped flower head. It is abundant along the rail corridor.

Globe Thistle

 A bit earlier in the season, one can find a lot of Dame's Rocket (Hesperis matrionalis) which occurs in both vivid pink and white. Its flowering period is long.....some may still be flowering into September.

Dame's Rocket

You've probably all seen those plants having a giant Dandelion-like seed head. It is the seed head of one of either Goat's Beard (Tragopogon dubius) or Common Goat's Beard (Tragopogon pratensis). They are common along roadsides, the inland part of sandy beaches, and certainly along railroads

 Goat's Beard

Common Goat's Beard

Some species that are not overly problematic in natural areas, but fairly common regardless are:

Everlasting Pea (Lathyrus latifolius)

Butter-and-eggs (Linaria vulgaris)

Rough-fruited Cinquefoil (Potentilla recta)

Teasel (Dipsacum sylvestris)

This next image shows the exotic Cabbage White butterfly (Pieris rapae) on the exotic Catnip (Nepeta cataria), while the image that follows shows a male and a female Cabbage White on Viper's Bugloss (Echinocystis lobata), also exotic.

 While it is nice to see butterflies flitting about, this European invader is one of the most widespread of butterflies, and it is a pest.....just ask any vegetable gardener or farmer, especially those producing cabbage, cauliflower, brussel sprouts, kale, broccoli, radish, turnip and other members of the Cruciferae family.

Then we get into some nastier, aggressive species. For example, White Mulberry (Morus alba). It is common along hedgerows, roadsides, urban and rural lots, railroad corridors, river valleys even some high quality natural woodlands. The dilemma is that the fruit is tasty to birds, racoons even humans. If you want to find birds in mid summer, find a few White Mulberry trees with abundant fruit as shown in the next image. There you will also find various fruit-eating birds, including American Robins, Gray Catbirds, Brown Thrashers, Cedar Waxwings and the like. However after the birds gorge themselves on these tasty berries, they leave and being members of the group of birds known as Passerines (perching birds), they perch on wires, fences, tree branches. And as the saying goes, what goes in must come out.....so when their digestive processes have completed the job, the seeds are pooped out wherever they happen to be sitting, sometimes several kilometres from where they originated. After a few decades, White Mulberry is all over the landscape.

White Mulberry

The unfortunate added dilemma is that there is a native mulberry in Ontario, the Red Mulberry (Morus rubra). It is limited in Canada largely to Fish Point Provincial Nature Reserve on Pelee Island, Point Pelee National Park, Rondeau Provincial Park and in the Hamilton area around the Royal Botanical Garden. There are a few other locations, but those are the main ones. Red Mulberry is now a legally endangered species, partly because of loss of the forested habitat which it prefers, but even more so because it hybridizes with the much more prolific White Mulberry. Even where Red Mulberry is relatively common, most specimens have some White Mulberry genes in them.

Another problematic plant species is White Sweet-Clover (Melilotus alba). It is a biennial, meaning that it takes two years to get to the seed-producing stage. Disturbed areas and even good quality natural areas such as tallgrass prairies, can have this species in abundance.

White Sweet-Clover

It can be difficult to find in an area one year as the first year's vegetative growth is under way. The following year it is super evident. It is a prolific seed producer, and the seed can last for years in the seed bank, so it is very hard to control. It also has a cousin, known as Yellow Sweet-Clover (Melilotus officinalis).

Abundant White Sweet-Clover

Another abundant but perennial species is Spotted Knapweed (Centaurea maculosa).

Spotted Knapweed

Spotted Knapweed in abundance

With these last two species, there is somewhat of an upside to them, fortunately. Pollinators love them! I have walked by some large expanses of both the White Sweet-Clover and Spotted Knapweed and been blown away by the number of bees, flies and butterflies that are present. In spite of the abundance of these plants, it almost seemed as if there weren't enough to go around....bees were almost lining up to find a spot on a flower head.

This brings me to what I consider one of the worst of the worst in terrestrial areas: Dog-strangling Vine, also known as Pale Swallow-wort (Vincetoxicum rossicum).

It is a perennial, a fast-growing vine and a prolific seed producer. It has seeds somewhat similar to milkweed, which are transported by air, so it can spread quickly. It also spreads very easily if even a small piece of a stem is transported to a potential site elsewhere.

Vincetoxicum rossicum

 Note its growth habit in the next image. As a vine, it climbs over existing vegetation, smothering it, to the point that it can be by far the most dominant vegetation at a site. Some places in urban areas are completely dominated by this beast.

It is not as abundant in Chatham-Kent as places farther east....yet. But I first noticed it in eastern C-K when I was doing some inventory work along this same railroad corridor in 2012. This year, I found it much more common between Chatham and Tilbury. It has probably been there for awhile, judging by its abundance, but it is only going to get more abundant. Effective controls for this species are not generally available. Even herbicides are only marginally effective.


There are many more exotic species present throughout southern Ontario and elsewhere. In fact on average even in a good quality natural area, the non-native plant species make up about 20-25% of the total list, but are often much greater in overall abundance. In highly disturbed sites such as railroad corridors, they can make up an even greater per cent of the plant list. They are here in abundance because of the great levels of alteration of the original landscape, courtesy of you and I and our predecessors. But that will be the topic of a future post.