The Miocene flora of Alum Bluff, Liberty County, Florida

Abstract

Abstract The plant fossils of Alum Bluff, northwestern Florida, provide a unique insight into the rarely preserved Miocene flora of the eastern United States. A century has passed since the introductory treatment on the fossil leaf flora of Alum Bluff. More specimens have accumulated over the past two decades, allowing for an updated evaluation of the megafossil flora following a recent study of the palynoflora. The strata consisting of poorly consolidated sand and siltstones with intervening clay layers, here recognized as the Fort Preston Formation of the Alum Bluff Group, are considered to be of Barstovian age (16.3–13.6 Ma), based on co-occurring mammalian remains. Here we recognize 36 kinds of leaves and 10 kinds of fruits and seeds, giving a minimum estimate of at least one fungus, one fern, one gymnosperm, 38 angiosperms and 7 unknowns. We also report one new species and two new combinations. These taxa augment those already reported based on pollen from the same strata, allowing us to portray the vegetation as elm-hickory-cabbage palm forest occurring near the coastline in a deltaic, pro-deltaic, or intertidal shore face environment. The results of a climate analysis of the Alum Bluff flora, using leaf margin and leaf area, give estimates of 19.0°C mean annual temperature and 116.0 cm mean annual precipitation.