Canada Thistle

This plant is pervasive along roadsides and in waste areas- you’ll often see them in colonies of multiple plants.  It started blooming in central Ohio in late May, and it’ll continue through the summer into early autumn.  It’s the most common thistle by a wide margin in this area.

It has multiple light purple blooms.

The flower head is small and compact, and not unattractive.

The leaves tend to be spiny and wavy, particularly on the lower stalk.  But this can vary among different populations.

Here in mid-summer, many of these plants have fuzzy seed heads replacing the flowers.  Each flower head can produce 40 to 80 seeds.

This is a very hardy plant…and now I’ll get to the sinister part of this blog title.  Unfortunately, Canada Thistle is an invasive species from Eurasia.  It most likely came to North America as a passenger in contaminated hay and grain seed in the 17th century.  It is hard to eradicate due to its deep roots that can keep it going for multiple years- cutting it down will not get rid of it.  Luckily this plant does best in waste type areas, and it is not without some benefit- some birds and insects feed upon them voraciously.

The bottom line with Canada Thistle is that very few people will say anything good about it- it is considered to be a weed even in its native range- it doesn’t get much lower than that, botanically speaking.  Googling this plant will bring up many pages on how to eradicate it, and I’ve seen it being controlled (presumably with herbicide) in the Metro Park system so that it doesn’t crowd out native plants.  But it looks like it will be around a while, and I bet birds such as finches would put in a good word for it.

A final note on the name- Canada is unfairly associated with the name of this plant that is probably a native of the Mediterranean and southeastern Europe.  It is also known as California Thistle- I bet California resents that- Prickly Thistle, and even Cursed Thistle (how’s that for a name?).    Multiple common names for any one species is one reason that Latin names for plant species are popular, which is a good idea but I don’t want to get too academic on this blog, so don’t worry 🙂