1. With the majority of people now living in urban environments, urbanization is arguably the most intensive and irreversible ecosystem change on the planet. 2. Urbanization transforms floras through a series of filters that change: (i) habitat availability; (ii) the spatial arrangement of habitats; (iii) the pool of plant species; and (iv) evolutionary selection pressures on populations persisting in the urban environment. 3. Using a framework based on mechanisms of change leads to specific predictions of floristic change in urban environments. Explicitly linking drivers of floristic change to predicted outcomes in urban areas can facilitate sustainable management of urban vegetation as well as the conservation of biodiversity. 4. Synthesis. We outline how the use of our proposed framework, based on environmental filtering, can be used to predict responses of floras to urbanization. These floristic responses can be assessed using metrics of taxonomic composition, phylogenetic relatedness among species, plant trait distributions or plant community structure. We outline how this framework can be applied to studies that compare floras within cities or among cities to better understand the various floristic responses to urbanization.