This is one of the oyster mushrooms. It is likely Pleurotus levis, but could also be the very similar Pleurotus dryinus (veiled oyster mushroom).
Pleurotus levis can be found on dead wood and also on live hardwoods from the central peninsula northward into north Florida and the panhandle. The range includes the entire eastern United States.
The cap is white to cream colored and velvety, yellowing with age. The white gills, which also yellow with age are decurrent down the stipe (stem, stalk).
P. levis has a partial veil with remnants being less persistent than on P. dryinus. The former also appears to tolerate warmer climates than the latter.
Phylum: Basidiomycota - higher fungi other than sac fungi
Genus: Pleurotus - oyster mushrooms
Pleurotus levis - GIANT PANUS
For a taxonomic tree and links to other fungi posted on Wild Florida Photo see the All Fungi at Wild Florida Photo page.