The structure of higher plants can be interpreted as being derived from a repetition of morphogenetic units called phytomers consisting of a leaf, a section of the stem, a lateral bud and – in grasses – adventitious roots. Such repetitive units of growth occur along the plant axis in a variety of forms with the potential for various phytomer components to be reduced, suppressed or modified. Particular phytomer variants are required, for example, to form specialized reproductive structures. The occurrence of phytomer variants that are typical for one part of a plant in other parts is called homoeosis and the study of such perturbations to the body plan of mutant plants provides promise for attempts to use molecular tools to trace the phytomer.