<p>Urban green spaces are essential components of green infrastructure and play a crucial role in supporting biodiversity and ecosystem services. This study examined spontaneous flora and insect pollinators in maintained urban parks and informal green spaces (IGSs) across eight types of urban development in Prague, Czech Republic. Floristic and entomological surveys were conducted at paired park and IGS sites, focusing on species richness, diversity, life forms, origin, invasive status, and Red List species. In total, 571 vascular plant taxa, including 380 native and 191 alien species (39 invasive), and 51 Red List species, were recorded. Overall, compared with parks, IGSs supported significantly greater plant species richness and diversity, although the differences varied among urban development types. Parks contained a higher proportion of native species, whereas alien and invasive species were more frequent in IGSs. Red List species were scarce and similarly represented in both habitat types. Pollinator abundance (honeybees, solitary bees, bumblebees, and butterflies) was generally higher in IGSs than in parks, with significant differences limited to certain urban development types. These findings suggest that habitat conditions influence their occurrence. Both parks and IGSs contribute substantially to urban biodiversity but differ in function: parks favour native species, whereas IGSs enhance overall species richness and pollinator abundance. These findings highlight the importance of incorporating informal green spaces into urban planning and biodiversity conservation strategies.</p>