Abstract:Genus size analysis is an important component in floristic research. The distribution pattern of genus size can reflect taxonomic diversity and phylogenetic diversity of a certain flora to some extent. In floristic studies, we cannot perform meta-analysis with mean genus size for its dependence on flora size. We applied logseries model to fit genus size distribution patterns of 8 spermatophyte floras in China, and achieved good fitting result. The goodness of fit R2＞0.99, indicating similar patterns between genus size distribution and species abundance distribution. Rarefaction analysis and correlation analysis showed that, mean genus size is not significantly correlated with its original values before rarefaction when the sampling size is small, while α index from the logseries model is stably correlated with its original values. Moreover, α index is significantly correlated with mean genus size for all sampling size, thus it could be taken as a stable index to describe the flora richness.