Although the basic body plan of flowering plants—similar to that of animals—is established during embryogenesis, plants continue to generate organs throughout their life cycle from groups of undifferentiated cells called meristems. In a typical flowering plant, two meristems are laid down during embryogenesis: the shoot meristem, which produces the aerial part of the plant, and the root meristem, which produces the subterranean root system. Several genes that control establishment and function of meristems have been discovered. The essential mechanisms, discovered in Arabidopsis thaliana, a relative of mustard, have been found to hold true for many other species as well, including snapdragon, tomato, petunia, and maize.