Fairy Ring

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Sometimes fungi grow underground in a circular shape and after a rain, the fruiting bodies, - commonly known as mushrooms - appear around the edge forming more or less a circle, called a fairy ring. Also, as can be seen here, the grass growing above the fungus might be lusher and greener than the surrounding area.
This fairy ring was seen while evacuating before hurricane Matthew in October of 2016.
For more information on fairy rings in Floirda visit UF IFAS Extension page on Fairy RIngs.
These might be Chlorophyllum mobybdites (syn: Lepiota morgani), Green-spored Lepiota, or another closely-related species. Note that this common fairy ring fungi of lawns is highly toxic and is known as the vomiting mushroom.

For a taxonomic tree and links to other fungi posted on Wild Florida Photo see the Fungi at Wild Florida Photo page.