Recent estimates of the number of described species of seed plant have varied by as much as 62%. The underlying methodology of these estimates is characterised and discussed. We present a revised figure for the number of seed plants based on estimating rates of synonymy in a sample of recently monographed taxa. We conclude that some recent figures overestimate the number of described seed plant species by more than 200,000. This discrepancy is explained by an overreliance on checklists and floristic studies that underestimate synonymy rates.

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