Aquatic Plants of the Eocene Republic, Washington Flora and Their Significance to Interpreting Ancient Lacustrine Environments

Studies of the Okanagan Highlands floras have focused primarily on the systematic affinities of key families (e.g., Rosaceae), or the use of fossil leaves to decipher paleoclimate. Often forgotten in these studies are aquatic taxa and their role in interpreting paleoenvironmental signals, a critical area of inquiry that has largely been overlooked. Because these plants have conservative morphologies and anatomies due to their adaptation to aquatic environments, their comparison with modern analogues can be made with relative certainly. Furthermore, the distribution of aquatic plants is strongly correlated with the duration and depth of water. The nature of the aquatic flora present within lacustrine depositional systems thus can provide additional data useful for interpreting sedimentary sequences. An emphasis of the present study is to determine the taxonomic affinities of aquatic plants present at one Okanagan Highlands locality (Republic, eastern Washington) and to interpret the associated subenvironments within the lacustrine sites. To date, such aquatic taxa as Nelumbo (Nelumboaceae), Nuphar (Nymphaeaceae), and the heterosporous water ferns Azolla and Salvinia provide unparalleled opportunities to accomplish this objective. A major goal of the present study is to use the interpretation of aquatic plant assemblages at Republic as a stepping stone for documenting lacustrine stages at this site. Additional data needed to accomplish this objective could be obtained from the fossil fish and insect faunas, in conjunction with analyses and correlation of fossiliferous units. Secondly, some taxa, such as Salvinia and Azolla have the potential for recording broader, global climate change signals discernable in Okamagan Highlands freshwater biotas that document plant response to critical environmental changes during the Eocene.