From Species Selection to Performance: A Review of Extensive Green Roof Suitability in the Mediterranean Basin

Mediterranean extensive green roofs are increasingly recognized as Nature-based Solutions for climate adaptation and urban sustainability, yet plant selection remains largely based on a limited set of drought-tolerant species. This review critically evaluates the biodiversity, biogeographical composition, and performance of plant species tested on Mediterranean extensive green roofs. A systematic analysis of 118 studies published between 2010 and 2025 identified 340 taxa belonging to 48 families, while species-level performance data were extracted from 92 studies. Research effort was strongly concentrated in Italy, Greece, and Spain, revealing significant geographical biases across the Mediterranean Basin. The species pool was dominated by chamaephytes and succulent taxa, particularly Crassulaceae, whereas Mediterranean endemics were underrepresented. Although native species accounted for most occurrence records, more than half of the tested taxa belonged to extra-Mediterranean chorotypes, indicating only partial geographical coherence. Performance assessments focused primarily on survival, growth, and drought tolerance, whereas reproduction, biodiversity outcomes, and ecosystem services were rarely evaluated. Several Mediterranean native species, including Helichrysum italicum, Salvia officinalis, Origanum dictamnus, and Crithmum maritimum, showed performance comparable to that of commonly used Sedum species, highlighting the potential of underutilized regional flora. The review supports a shift from establishment-based plant selection toward ecologically coherent approaches that integrate biodiversity, biogeographical affinity, ecosystem functioning, and long-term resilience.