For a few years I've been waging a war, in my garden, against the invasive Canada thistle. It spreads by an underground root system and, even if you pull out all the visible weed, if you leave even an inch long piece of root in the ground, it will spring back from that. This year I thought I was beginning to get the upper hand then I discovered that a new species seems to have moved in to fill the gap. Arrgh....!
