Cities represent enviroment for most of Europe's human population. Spatial pattern of cities' environmental as well as socioeconomic features affect plant biodiversity. We analysed a floristic mapping dataset of the city of Ljubljana (Slovenia) and asked what affects the spatial differences in the presence of different categories of species: species according to residence time and endangered and thermophilic species. To explain the proportions of these species groups in grid cells, using Generalized Additive Models, we tested the effects of three categories of predictors: i) urban structure, represented by the distance from the city centre, population density, soil sealing, and quality of residential environment index, ii) habitat predictors, represented by habitat diversity and geologic diversity, and iii) environmental conditions, represented by urban heat island (UHI). Species richness decreases with the distance from the city centre and is highest in the cells with intermediate habitat diversity. Number of species is highest within city parts of highest quality of residential environment index and lowest in parts with UHI effect. Proportion of native species is positively related to habitat and geologic diversity. The proportion of archaeophytes is higher where habitats are more diverse and increases with the distance from the city centre. Grid cells with highest proportion of neophytes are located in the most built-up areas and in the city centre, which is positively associated with soil sealing, but negatively with UHI. Thermophilic species are positively associated with soil sealing. Endangered species have uniform distribution pattern and their proportion is negatively associated with distance from the city centre and soil sealing. A grid cell with the highest proportion of endangered species includes two protected areas with wetland habitats. Calculated ecological indicator values show correlation with soil sealing and habitat diversity. Some of the results are in line with well-established patterns from other cities, while others reflect certain specific features of Ljubljana, e.g. forested hills close to the city centre. The identified hotspots of city's plant species richness can serve in the argumentation of future urbanistic planning.
