XVI International Botanical Congess

Generic similarities between the Oligocene flora of Europe and North America are pronounced. Some taxa were circumboreal, while others were confined to North America and Europe (e.g., Tetraclinis, Mahonia, Cedrelospermum). Closely similar taxa, even shared species (Tetraclinis salicornioides, Cercidiphyllum crenatum) may indicate migration via the North Atlantic during or prior to early Oligocene. Due to global cooling near the end of the Eocene, shared elements include more mesophytic than warm-adapted taxa. More thermophilous plants survived in Europe (Eostangeria, Eotrigonobalanus, Raskya, Sloanea). Some sclerophyllous elements (e.g. Comptonia schrankii, Zizyphus zizyphoides) developed exclusively in the Old-Mediterranean flora. The occurrence of these and other endemic genera in both continents during the Oligocene suggest some floristic provinciality.