growing in large, dense clumps on edges of salt marsh
De Soto Monument, Manatee County, Florida
Borrichia frutescens (I think). 3.5 cm across, ~60 cm tall, growing in a dense stand near the edge of a lagoon. I left it uncropped to show the leaves, but it's super in original size.
Borrichia is a genus of flowering plants in the aster family, Asteraceae. It is named for Danish physician Ole Borch (1628-1690). Members of the genus are commonly known as seaside tansies. They are native to the United States, Mexico, and the Caribbean.