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Mechanisms underlying large‐scale spatial patterns of species richness are one of the central issues in ecology. Although contemporary climate, evolutionary history, and historical climate change have been proposed as drivers of species richness patterns, variation in the relative importance of different factors remains a major challenge. Here, using newly compiled distribution data with a spatial resolution of 100 × 100 km for 43 023 angiosperms plant species in east Eurasia, we mapped species richness patterns for plants with different growth forms (i.e. woody versus herbaceous) and range sizes (i.e. wide‐ranged versus narrow‐ranged species), and compared the relative importance of the four hypotheses in explaining these patterns, i.e. freezing tolerance hypothesis, historical climate change hypothesis, Janzen's hypothesis (predicting that climate seasonality and topography determine species richness patterns), and diversification rate hypothesis. We found that species richness of all angiosperm plants presented a clear latitudinal gradient and was highest in southwestern China and Central Asian mountains. Notably, species richness patterns and their dominant drivers differed between species groups. Historical climate change was the dominant driver for richness patterns of all and herbaceous species. The freezing tolerance hypothesis dominated the drivers for all woody species, while Janzen's hypothesis dominated narrow‐ranged woody and herbaceous species. Our study suggests that different hypotheses contribute to large‐scale plant richness patterns via their effects on different plant groups. Our results did not support the diversification rate hypothesis, but demonstrated the high importance of historical climate change to plant diversity in east Eurasia, providing new perspectives on the mechanisms of plant diversity patterns in this continent. [ABSTRACT FROM AUTHOR]