In my post on October 26, about the third walk I took at KSR on August 23, I included this photo of a
vine I didn’t recognize, and couldn’t remember seeing before:
and asked if anyone knew what it was. My thanks to Janet
Inksetter and Helen Mills both, who told me it is dog-strangling vine, a perennial, non-indigenous plant of the milkweed family, first described (botanically) in
the Kiev area of Russia, and thought to be endemic to the Caucasus and Black
Sea region. It is now not only found but deemed invasive throughout southern
Ontario, as well as in Connecticut, Massachusetts, New Hampshire, New York, and
Wisconsin.
The vine is also known as European swallow-wort and pale
swallow-wort, but dog-strangling vine is more vivid and memorable a name. It
connects to the binomial term “cynanchum,” which is derived from Greek words
meaning “dog” and “strangle” or “poison”. From what I’ve been able to discover
there’s no record of the vine snaking out and snaring a dog, or any other
animal, but it is possible it was used as an animal poison in the past, since it
has toxic qualities.
In spite of the possible poison connection I think the name has a misplaced hyphen. The plant is a twining vine (twining left to
right!) that winds itself around whatever it climbs, and eventually grows so
densely that it strangles other plants, producing a monoculture. So “strangling-vine”
is more accurate to its behavior. Where “dog” fits, in my scenario, is in the
plant’s following at the heel of settler/immigrant culture: its origin in Ontario is
likely as an escape from gardens.
As the photograph above shows, the leaf is attractive, and
since the vine grows thickly it would be attractive to gardeners. I read one
account that suggested it was brought in for the fluffy seeds that were used
for filler in life jackets during the war, but I haven’t been able to verify
that. Although it grows
less quickly in shaded areas—its native turf appears to be grasslands—it can
grow almost everywhere and is commonly discovered in backyards, pastures,
woodlands, and alongside streams.
Within the Toronto region dog-strangling vine grows
throughout the Don and Rouge watersheds, along the Humber, and in most natural
areas of the Oak Ridges Moraine, including KSR. There’s a good write-up tracing
the species presence in southern Ontario and what was known (by 2007) of its spread
and behaviour at
I went looking
for that patch of the vine again a couple of weeks ago and found it. Here’s
what it looks like now—
and in this
form I do remember seeing it in both Sunnybrook Park and along the Rouge.
Like most
non-native invasive plants, dog-strangling vine has no known natural controls.
It spreads largely, and very successfully, by seed (germination plus or minus
50% in optimal conditions), but it also can move via rhizomes, and, as the
Rouge Park report makes clear, its behaviour may have changed over time.
If you
do an internet search for Cynanchum rossicum you’ll find many pages warning of its ability to
take hold and take over with what are expected to be dire consequences for
species diversity. It does in fact constitute a threat to insects—Monarch
butterflies being a particular concern because they lay their eggs on the
plant, but the caterpillars can’t survive on it—as well as other plants.
An excellent
species account is available at: http://www-personal.umich.edu/~rburnham/SpeciesAccountspdfs/CynarossAPOCFINAL.pdf
I asked Art
Weis, the Director at KSR, about the vine and about the general practice here regarding invasive plants. Here’s what he said:
We are starting a co-operative project with
Seneca College on dog strangling vine. It is getting to the point where some
control measures will be needed to keep it out of the old growth forest. The
first step with Seneca is to map its occurrence on the west side of Dufferin Street.
However, we do not try and eradicate invasives because they offer potential
research projects.
The mapping
project will begin next June, in the area where I took these photographs.
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