Weeds in our bonsai actually grow faster than the speed of light, and spread faster than half melted butter. And I think clover is close to the worst. We are now in the midst of the worst season for weeds, late spring-early summer. You can pick out all the weeds in a bonsai today, and by the end of the week, each weed you pulled out has resulted in the formation of 20 tiny little embryonic leaflets popping out of the ground. These new little leaflets are just small enough that you can't quite get a hold of them.
Clover is bad because they have such giant roots.
Sometimes I'll get the whole root out, and it turns out to be so massive I feel like I should wire it up, style it and pot it. About the only weed I hate worse is one I don't know the name of, but looks like a microscopic spider plant. It sends out an arm which creates a clone an inch or two away. Each plant then sends out another, and pretty soon your whole pot is filled with these things. It actually brings pain to my fingertips to pull one out.