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Increased stormwater runoff from impervious surfaces is a major concern in urban areas and green roofs are increasingly used as an innovative means of stormwater management. However, there are very few studies on how different vegetation types affect the amount of water runoff. This paper describes an experiment that investigates the influence of plant species and plant diversity on the amount of water runoff from a simulated green roof. Twelve species were selected from the three major taxonomic and functional plant groups that are commonly used for extensive green roofs (forbs, sedum and grasses). Four species were chosen from each group and planted in combinations of increasing diversity and complexity: monocultures, four-species mixtures and twelve-species mixtures. The results showed that there was a significant difference in amount of water runoff between vegetation types; grasses were the …