XVI International Botanical Congess

Probabilistic similarity indices show statistically significant similarities and differences among floral assemblages, and allow phytogeographic analysis of intervals like the Late Siegenian-Emsian, in which sampling intensity may influence the amount of differentiation. Analysis of Late Siegenian-Emsian fossil assemblages at the generic level using the Raup and Crick probabilistic similarity index reveals six regions with significant endemism: W. Laurussia, E. Laurussia, Siberia, the Pribalkash terrain, China, and Australia. Laurussia and Siberia are strongly linked. The presence of Hedeia and tightly clustered synangia-like sporangia in Australia (Yarravia) and China (Celatheca) suggests similarities between these two areas.