XVI International Botanical Congess

Recent work on anatomy of Argentinia fossil cycads revealed anatomical details allowing assignment of the fossils to extant groups based on synapomorphies. That these fossil cycads are indeed cycads is supported by the possesion of among other characters girdling leaf traces, a cycad synapomorphy. Menucoa and Bororoa have synapomorphies, e.g. presence of inverted, pith bundles, with Encephalartineae. Mesodescolea has leaf epidermal cell features that are a synapomorphy with the extant genus Stangeria. These data show that fossil cycad genera can be placed with extant genera and that at least two major groups of cycads, Stangeriaceae and Encephalartineae, were present in South America in the Triassic through the Tertiary and are now extinct there. Comparative morphology and anatomy of extant and fossil cycads revealed synapomorphies with Bennettitales.