The Mediterranean Basin biodiversity hotspot covers around 2,300,000 km². Here, occurr mafic and ultramafic outcrops (serpentine outcrops s.l.), naturally fragmented ecosystems that host a rich flora adapted to their edaphic extreme conditions. Moreover, these outcrops are also subjected to pressure from metals and rare earth elements extraction. Despite the numerous studies on individual or local outcrops, has been lacking a comprehensive assessment of the serpentine’s outcrop distribution, ecological characteristics, and conservation status across the Mediterranean Basin. This study provides the first harmonized digital map of Mediterranean Basin serpentine outcrops and investigates their climatic, geographical, and protection status.

Serpentine outcrops cover 24,056 km² (the 1.15% of the Mediterranean Basin), of which 5,255 km² (22%) fall inside protected areas, including just 44 of the 94 mapped outcrops. Nearly 3,126 km² (60%) are concentrated in just three complexes: Troodos (Cyprus), Pindos and Mirdita (Greece and Albania). Regarding the ten Mediterranean biodiversity hotspots (area of 417,267 km²) identified by Médail (1997), 34 outcrops are inside and cover 11,442 km² (2.7%).

Most outcrops occur at medium elevations and have a typical sub-Mediterranean climate, with moderated temperatures, annual precipitation around 700mm, high temperature seasonality, and relatively low climate change velocity. Human footprint values are generally lower than the Mediterranean ones.

We compiled records of 521 taxa for 42 outcrops, represented by Brassicaceae (19%), Asteraceae (17%), Caryophyllaceae (10%) and Poaceae (5%). According to the IUCN Red List, 3% of the taxa are assessed as Critically Endangered, 7% as Endangered and Vulnerable and 6% as Near Threatened while 58% as Not Evaluated.

Our results highlight important conservation gaps despite the exceptional biodiversity hosted by serpentine ecosystems. The harmonized database and digital map provide a baseline for future ecological, biogeographical, and conservation studies, supporting management and protection of the Mediterranean Basin serpentine outcrops.