Urban areas face significant environmental challenges, requiring integrated solutions. As urbanization increasingly impacts biodiversity, cities must contribute to its conservation as per global goals. Nature-based Solutions (NbS) are widely adopted to tackle urban challenges. However, evidence for their success in urban biodiversity conservation remains weak. Although NbS are defined by using native biodiversity for net ecosystem services benefits, many NbS projects feature exotic and invasive species. We conducted a systematic literature review and qualitative synthesis, following PRISMA guidelines, on 67 studies published in English (2013-2023) from the Global South to assess urban NbS biodiversity outcomes across 83 unique cities. Only 55 studies evaluated biodiversity outcomes, with just 43% identifying specific flora or fauna. The NbS types included blue-green infrastructure, urban green spaces, urban forests (each 22%), and green roofs (18%). Our analysis revealed a critical methodological inadequacy: measuring biodiversity co-benefits with pre- and post-implementation data or evidence was rare. Crucially, not one study included necessary baseline assessments to effectively measure biodiversity gains. Furthermore, native biodiversity, mentioned as a co-benefit, was often poorly described. Through our systematic literature review, we found 27 studies mentioning use or presence native species and 16 studies mentioning exotic species in the NbS implemented. We found that including an ecologist in the author teams positively influenced the reporting of specific species (p<0.05). In the absence of robust data, our ability to integrate NbS into global conservation goals is weakened. Our synthesis highlights key gaps, best-practices and recommendations to strengthen native biodiversity considerations in NbS in the global south.