Extreme greenhouse warmth triggered the two major floristic turnover events of the past 120 million years.

Extreme global warmth during the mid-Cretaceous and early Cenozoic triggered major floristic turnover in all land plant groups, with elevated first and last appearances.

• Why it matters: Understanding how past climate extremes influenced plant evolution helps clarify the role of climate in shaping terrestrial biodiversity and the timing of major ecological transitions.
• What they did: Sampling-standardized analyses of spore-pollen fossil records from high and low palaeolatitudes were used to identify periods of floristic turnover, focusing on the mid-Cretaceous and early Cenozoic.
• The result: The findings suggest that land plant diversity is ultimately controlled by global climate state, with extreme warmth episodes driving synchronized turnover across latitudes.