Understanding how geographical patterns of plant richness are established is a key scientific question in ecology and biogeography. Climate factors, such as environmental energy, water availability, and rainfall seasonality, have been widely proposed to account for geographical patterns of plant richness at large scales. Using a compiled distribution data set of 3166 native woody dicotyledons across 732 calibration grids at the county level in humid regions of China, we explored the geographical pattern of woody dicotyledon richness and its relationship to climatic variations, especially the Asian monsoonal climate. We found that species richness decreases with increasing latitude. Our study indicates that water availability (particularly mean annual precipitation, MAP) is the major abiotic factor in determining large-scale distribution patterns of species richness. Moreover, the seasonality of rainfall variables under the Asian monsoon climate largely contributes to species richness, because species richness correlates more significantly with precipitation during the three driest consecutive months (P3DRY) than precipitation during the three wettest consecutive months (P3WET). Therefore, we conclude that woody dicotyledon richness in humid regions of China is mainly affected by the Asian winter monsoon. Copyright (C) 2020 Kunming Institute of Botany, Chinese Academy of Sciences. Publishing services by Elsevier B.V. on behalf of KeAi Communications Co., Ltd.