Palaeobotanical experiences of plant diversity in deep time 1: How well can we identify past plant diversity in the fossil record?

Palaeobotany and palynology are the main direct sources of evidence for studying vegetation diversity dynamics through geological time. However, plant fossil diversity is affected by various factors other than vegetation diversity, which need to be taken into account in such studies. The use of fossil-taxa will potentially inflate perceived plant diversities, requiring taxonomic lists to be normalised. Autochthonous floras provide the most direct evidence of vegetation diversity but these are rare; most plant beds are allochthonous with plant remains that have been subjected to varying levels of fragmentation, transportation and time averaging. Local-scale vegetation diversity is especially difficult to determine from the fossil record, even with rigorous sampling protocols and detailed sedimentological analysis. Landscape-scale and regional-scale vegetation diversities are more reliably determined but usually at the rank of family. Macrofossil and palynological data tend to reveal evidence of different aspects of plant diversity, and the best results are obtained if the two diversity signals are integrated. Despite the inherent difficulties, the plant fossil record provides clear evidence of the dynamic history of vegetation through geological times, including the effects of major processes such as climate changes and mass extinctions.