I saw these locally and they look like some sort or Mimosa. I think they are from seeds. I don't think they are winter hardy here. What are they?

No, I don't think it's Mimosa...Maybe Pride of Barbados? Just guessing because I've never seen one. But we do have Mimosa. That's not it.

edit...I don't think the flowers are right for the "POB"...still searching...

Looks like Sesbania punicea.

I think that's it! If you start these from seeds, will they bloom that same year? I'm thinking about getting some seeds. These look great with the red tropical milkweeds!

Yup, that's it! And there aren't any pics in the DB! They are beauties!

It will mature fully from seed in one year, but it's highly invasive and will crowd other plants out if given a chance.

I bet our winters kill them out. These are at the Experiment Station here.

Not only highly invasive but toxic to birds and mammals. As beautiful as this plant may be, I would not encourage you to grow this in your yard. Also, the seeds have the ability to float so during a big rain event the seeds could travel, end up in a storm sewer and become a problem for the river environment. The winter may well kill the plant but the seeds will germinate in the spring and are viable for several years.