Ecological species groups and trait convergence of urban spontaneous plants: Evidence from 16 cities within biodiversity hotspots

Urbanization profoundly reshapes the diversity patterns of urban spontaneous plants, which are effective indicators of urban environmental change. Categorizing ecological species groups (ESGs) are crucial for understanding species-environment relationships and for supporting biodiversity conservation. In this study, 586 spontaneous plants across 16 cities in Yunnan province, China, were classified into four ESGs using a two-way clustering approach that integrates urban-rural gradients (expressed by the distance to city boundary) and human activity intensity (the proportion of impervious surface), and their indicator species were subsequently identified. The four ESGs—disturbance-sensitive urbanphob plants (DSUP, 29.5 %), disturbance-tolerant urbanphob plants (DTUP, 26.5 %), disturbance-tolerant urbanophil plants (DTUO, 22.9 %), and disturbance-sensitive urbanophil plants (DSUO, 21.2 %). Trend analysis revealed that only DSUP shows consistent response across both urbanization gradients, suggesting that relying on a single urbanization metric may bias in ESG classification and obscure the complexity of plant responses to urbanization intensity. Functional diversity metrics combined with a null model approach revealed significant trait convergence within ESGs (except DSUO) and clear variability among them, suggesting a convergence in traits driven by urbanization filtering effects. Our findings revealed that indicator species of ESGs are predominantly by herbaceous, native, and autochorous species. Nonetheless, trait variations still emerged along disturbance gradients. In particular, fruit type composition varied substantially among indicator species of ESGs, with caryopsis predominated in DSUP ('60 %), pod in DTUP ('25 %), capsule and achene in DTUO (25.0 % and 20.8 %, respectively), and caryopsis (29.4 %) and nut (23.5 %) in DSUO. Our study emphasizes the difference in species adaptation strategies at different levels of urbanization, underscoring the imperative to develop appropriate habitat conservation strategies that align with species-specific habitat preferences.