10. Scotch Thistle
Scotch Thistle (Onopordum acanthium)
- Blooms from May to June
- Can grow 2 to 4 feet the first year
- Can reach 10 feet in the second year
- Large amount of soft white hair on upper leaf surface
- Winged tissue along stem
- Purple flower
- Form dense, practically impenetrable stands
Photo by Eric Coombs, Oregon Department of Agriculture