Assessment of vegetation biodiversity of twelve extensive grasslands as Biodiversity Promotion Surfaces (BPS) in Geneva. A study on twelve Biodiversity Promotion Surfaces (BPS) of extensive grasslands in the canton of Geneva has enabled to characterize these surfaces from their vegetation point of view. The selection was based on two criteria having a potential influence on their biodiversity: (1) their size (<3'000m2 vs > 9'000m2) and (2) their level of botanical quality as defined by official criteria (Q1 vs Q2). The standardized methodology developed in this study proved to be optimal for the exhaustive characterization of vegetation in these surfaces, and is partly based on the method established by the Canton for granting the higher quality level. This methodology consisted in the creation of vegetation inventories within four quadrats of 1m2 each per vegetation formation. This sampling was complemented by a more comprehensive inventory covering the entire meadow by listing non-inventoried taxa in the quadrats. These botanical inventories allowed to verify that quality 2 BPSs are botanically richer than quality 1 BPSs (3 more species in median value). The size of BPSs was not linked to this richness and only had a small influence on specific composition. These inventories also enabled to identify indicator species based on size and BPS quality, allowing to detect changes in somewhat long term.