After all, just because the frost killed all purple flower invasive weeds doesn't mean it got to their seeds or root fragments, too. Given that, it's pertinent to learn to spot the purple bloomers ...

this biennial weed is common in pastures and open fields. A tough perennial with thistle-like purple flowers. It's invasive ...

Flowers are unisexual, on separate plants; flowers purple (occasionally white ... but still maintain itself. This aggressive weed is difficult to control; for example, breaking up the roots by plowing ...