Global species numbers of fungi: are tropical studies and molecular approaches contributing to a more robust estimate?
Recent estimates of the global species numbers of fungi suggest that the much-used figure of 1.5 million is low, and figures up to 5.1 million have been proposed in the last few years. Data emerging from tropical studies, and from large-scale sequencing of environmental samples, have the potential to contribute towards a more robust figure. Additional evidence of species richness is coming from long-term studies of particular non-tropical sites, and also from molecular phylogenetic studies revealing extensive cryptic speciation. However, uncertainties remain over fungus:plant species ratios and how they should be extrapolated to the global scale, and also as to the geographical distribution of fungi known only as sequences. Also unclear is the extent to which figures should be modified to allow for insect-associated fungi. The need for comprehensive studies, especially in the tropics, to address the uncertainties used in past extrapolations, is stressed. For the present, it is recommended that the phrase “at least 1.5, but probably as many as 3 million” be adopted for general use until some of the current uncertainties are resolved.