I bet it's gonna be....Bidens (not sure of species)..aka beggarticks. Expect yellow cosmos (close cousin) like flowers starting soon till frost.

What dbarron said.

Beggar's tick is Bidens Alba. Probably the most common weed in florida.

Agree with Bidens.

Bidens frondosa or B. vulgata. Don't expect showy flowers.

My Bidens (course I'm out West), are quite showy...
The species I have seen is B. aristosa...

Thank-you everyone! Bidens it is! I don't think the leaves or stems match those of B. alba...the stems are red and green. I also understand that B. frondosa and B. vulgata are very similar....am I right to assume that I need to wait 'til it flowers to count the number of leafy bracts around the flower to be able to determine which it is? I don't care much about showy flowers but w/limited space in this disturbed area I prefer species like Joe Pye, goldenrod, Asclepias...I read that quite a few species eat the foliage of beggar's tick so as long as it doesn't out compete everything else I'll keep it :) Thanks!

It will quite successfully reseed...in a moist environment.