Analyses of the phylogenetic relatedness of plant communities in urban areas have great potential to inform future diversity planning in expanding or new urban areas. The influences affecting the number of taxa found in urban areas and their phylogenetic diversity remains unclear. Both native and exotic (or imported) plant species can be found in urbanized areas: some grow spontaneously, and some are cultivated. These groups likely have different drivers: cultivated species diversity may be dependent on city wealth and the nature and extent of green space within those urban areas. In contrast, spontaneous species diversity may be more closely related to the constraints of climate. In this study, we analyzed the drivers of plant taxonomic richness and phylogenetic diversity of five groups (native-spontaneous, native-cultivated, exotic-spontaneous, exotic-cultivated and all) across 18 different cities in China that spanned different climate zones and socioeconomic status. We used both fieldwork and existing literature in our study. We constructed general linear models to assess whether the number of taxa and the phylogenetic diversity of plant life in each of the five studied groups could be related to any of two biophysical variable Mean Annual Temperature (MAT) and Mean Annual Precipitation (MAP as well as two socioeconomic variables, Gross Domestic Product (GDP) and Urban Greening Percentage (UGP). We identified 5163 plant species (229 families and 1730 genera) in the combined final plant species list from the 18 Chinese cities. The composition of all plant species was positively correlated (p < 0.01) with both MAP and MAT. Very few diversity metrics seemed to be related to the environmental factors tested, but the patterns were consistent with expectations. The Net Relatedness Index (NTI) of native cultivated species was negatively related to socioeconomic variable UGP (greater overdispersion with greater UGP), whereas the family richness and phylogenetic overdispersion of urban spontaneous plant species were positively related to the climate variable MAT. These findings might indicate long-term urban legacy effects over the course of centuries as have been observed in other world regions having a long history of urbanization.