The key difference between angiosperms and gymnosperms is how their seeds are developed. The seeds of angiosperms develop in the ovaries of flowers and are surrounded by a protective fruit. Gymnosperm seeds are usually formed in unisexual cones, known as strobili, and the plants lack fruits and flowers. Additionally, all but the most ancient angiosperms contain conducting tissues known as vessels, while gymnosperms (with the exception of Gnetum) do not. Angiosperms have greater diversity in their growth habits and ecological roles than gymnosperms.