<p>Urbanization, characterized by increased impervious surface coverage (ISC), higher temperatures, and reduced vegetation, presents both challenges and opportunities for studying plant responses to environmental stress. This study examines how urbanization influences the phenotypic expression of functional traits in an alien herb (<i>Ruellia nudiflora</i>) across five tropical cities in the Yucatán Peninsula, México. Given environmental contrasts between rural and urban areas, we predicted consistent patterns of trait divergence across cities. Our results confirm that urban environments exhibit higher ISC, lower vegetation cover, and increased dry heat compared to rural settings. Urban plants showed lower trichome density, thinner leaves, higher total phenolics and leaf C%, and a lower C:N ratio, while leaf N% remained similar across environments. However, only thinner leaves, lower C%, and lower C:N in urban plants were consistent across all cities. A trade-off between structural and chemical traits was evident, where increased leaf thickness and trichome density correlated with reduced total phenolic content. The expression of this trade-off, along with leaf C%, was driven by dry heat, though its effects are mitigated in urban environments. Notably, these patterns remained consistent across cities, highlighting urban ecosystems as valuable models for studying plant stress-response syndromes and predicting trait shifts under environmental change. Thus, urban ecology is a powerful framework for understanding plant strategies to cope with stress and for improving trait-based predictions in a rapidly changing world.</p>