I have a hard time identifying things on leaves alone, but it does look like Ragweed I’ve seen.

Not an Ambrosia species.

Could be wildly wrong, but I get a possible sense of something in the Verbenaceae. Perhaps a vervain???? Is there any chance of a close up showing the tips of the stems?

I've looked at every Verbena species that occurs in Texas and can't find a match. Verbena bracteata has similar leaves, but only grows 20 inches and is prostrate in growth pattern. Try to get more photos when it's in bloom.