horseweed, Conyza canadensis

Horseweed has tiny little flowers in heads hardly a quarter inch long. But there can be hundreds on one plant. They may be tiny, but they're very assertive. This native will grow in almost any dry spot. I imagine it's called horseweed because it often shows up in pastures or other occasionally nasty spots. The little seeds with fluff attached can blow long distances before finding a good bare spot, so this is an early colonizer in newly disturbed places. It grows in every state and province except LB and YT, on SPM, and now most anywhere else around the world. Monroe Co MI, 8/25/13.