Thinking Hylodesmum glutinosum, though it is hard to see all the parts. Could also be a Desmodium sp.

Porterweed? Here is a link that might be useful: Stachytarpheta spp.

Yes, the seeds. I believe it has to be something in the Asteraceae which flowers late in the growing season. I've collected seeds in my garden from Vernonia which looks similar to your picture. It's only a hunch since we missed the flowers.

Depending on your climate they will grow and flower all year. But they also self seed and will spread to wherever seeds might be washed to by rain.