21. Iris
Few summer perennials have quite as many color and pattern options as the Iris. You can always identify an iris from a distance by their beautiful spear-like green leaves which can get surprisingly tall. These stalks are soon accompanied by beautiful bearded flowers in shades ranging from purest white to almost true black. They also have literally everything in between except for, perhaps, true green.
Irises spread beautifully and can be divided in the autumn, so set aside some space for a large Iris bed! They are also another top option for weddings if you have a color scheme to match.