Jun 06 2010
Though we call it Canada Thistle, Cirsium arvense is badly misnamed. Native to Europe and northern Asia, it’s now found as far away as Australia and New Zealand, and it’s never welcome. It’s invasive nearly everywhere it grows.
Some of Canada Thistle’s other names are more descriptive: Hard Thistle, Creeping Thistle, Cursed Thistle. It spreads by seeds and through its “creeping” root system that extends horizontally for 15 feet or more. Each plant produces only male or female flowers so a clump can be isolated and not be pollinated. No matter. It’s perennial, its roots spread, and it chokes out less aggressive plants.
Watch for Canada Thistle’s violet flowers by roadsides, in fallow fields and in disturbed sunny patches. When you find it, there’s one bit of good news to keep in mind. Canada Thistle provides food for Painted Ladies and American goldfinches.
Goldfinches nest when the thistle blooms.
(photo from Wikipedia. Click on the image to see the original.)