A sample of a sedum green roof on test in Riseley, kindly supplied by Wallbarn Ltd. The sedums are growing in a crushed recycled brick growing medium, on top of a piece of fleece. The "egg box" drainage bottom layer, visible in the bottom left of the photo, retains a small amount of rain water in the dimples.
Sedum is the large stonecrop genus of the Crassulaceae, representing about 400 species of leaf succulents, found throughout the northern hemisphere, varying from annual and creeping herbs to shrubs. The plants have water-storing leaves.