Also known as the Tunic Flower, this low-growing plant will make a lovely addition to any green roof. The flower stems shoot up from the dense grass-like foliage, reaching almost a foot in height and displaying gorgeous white or pale pink flowers. Blooming throughout the summer, this plant loves full exposure to the sun. A hardy perennial that is drought tolerant and can withstand harsher temperatures or poor soil. It grows best in hardiness zones four through seven. The tunic flower has relatively shallow root systems, allowing them to be effective for ground cover. Although native to Eurasia, it has been naturalized in northeast America.