It is interesting to me that the word bidens comes from Latin meaning two (bi) teeth (dens). If you notice the seeds, they sure enough have two little teeth that cause them to stick to your clothes like Velcro. Because of this characteristic of hitching a ride on your clothes and clinging tightly, the flowers have earned the common name "tickseed" or "beggarticks". ("Spanish needles" are in the same genus.) Here are some pictures we took last September. I think my son took the good shots, so probably most or all of these are his. I think these may be bidens aristosa, which is listed in the NC DOT wildflower program info.
Do you notice the flowers along the roadside? (Don't let them distract your driving.)