The composition and seasonality of the benthic algae of the Florida Middle Ground, an offshore area of extensive reef outcroppings, 25 to 60 m deep in the eastern Gulf of Mexico, are described. Collections and observations were made by SCUBA diving during June, July, and September, 1971, and January 1972. Ninety-one algal species (92 taxa) were obtained, including 6 species newly reported for Florida and the eastern Gulf of Mexico. The flora is predominantly tropical, with Caribbean affinities. Marked seasonal differences in species diversity and abundance were present. An extensive or well-anchored holdfast system was a common feature of those species which appeared to be perennial.