INVESTIGATION OF SEDIMENT CORES FROM FLORIDA WATERWAYS FOR THE PRESENCE OF PISTIA STRATIOTES L. SEEDS

Pistia stratiotes L., commonly known as water lettuce, is currently ascribed a non-native status and is often managed as an invasive weed in Florida’s waterways. However, recent genetic studies and analysis of paleo-sediments demonstrate a native status of Pistia in Florida. We are further investigating the native status of Pistia by inspecting a series of soil cores from settings with high potential for the paleo-occurrence of Pistia for the presence of Pistia seeds, which are identifiable by their barrel-shaped morphology. Thus far, we have analyzed 60 surface sediment samples from sites on Lake Beresford and Gum Slough, FL, from locations where Pistia plants are abundant at the surface. Three Pistia seeds were found from a total of approximately 7676cm³ of sediment analyzed (= 1 seed/2559cm³), suggesting that Pistia seeds in sediments are relatively rare even at sites where the plant is abundant. Thus far, analysis of 48cm to 100cm length sediment cores from seven different Florida field sites (near Volusia Blue Spring, DeLeon Spring, Alexander Spring, Wekiwa Spring, Gum Slough, Lake Woodruff Wildlife Refuge, and Lake Ashby) has yielded six Pistia seeds from approximately 19,269cm³ of sediment analyzed (= 1 seed/3212cm³). These seeds were found at various sample depths, from near the surface to nearly 100cm core depth. Future work will focus on collecting deeper cores that can potentially yield older Pistia seeds for radiocarbon dating, thus further establishing the antiquity of the species in Florida’s waterways.