•Tropical grassy biomes are extensive and critical to human livelihoods.•The definition of these grassy systems is inconsistent and misleading.•We discuss novel threats linked to problems with biome definition.•The assumption that ‘more trees are better’ does not hold for tropical grassy biomes. Tropical grassy biomes (TGBs) are globally extensive, provide critical ecosystem services, and influence the earth–atmosphere system. Yet, globally applied biome definitions ignore vegetation characteristics that are critical to their functioning and evolutionary history. Hence, TGB identification is inconsistent and misinterprets the ecological processes governing vegetation structure, with cascading negative consequences for biodiversity. Here, we discuss threats linked to the definition of TGB, the Clean Development Mechanism (CDM) and Reducing Emissions from Deforestation and Forest Degradation schemes (REDD+), and enhanced atmospheric CO2, which may facilitate future state shifts. TGB degradation is insidious and less visible than in forested biomes. With human reliance on TGBs and their propensity for woody change, ecology and evolutionary history are fundamental to not only the identification of TGBs, but also their management for future persistence.