Reversion from floral to vegetative growth is under environmental control in many plant species. However the factors regulating floral reversion, and the events at the shoot apex that take place when it occurs, have received less attention than those associated with the transition to flowering. Reversions may be categorized as flower reversion, in which the flower meristem resumes leaf production, or inflorescence reversions, in which the meristem ceases to initiate bracts with flowers in their axils and begins instead to make leaves with vegetative branches in their axils. Related to these two types of reversion, but distinct from them, are examples of partial flowering, when non-floral meristems grow out so that the plant begins to grow vegetatively again. Anomalous or proliferous flowers may form as a result of unfavourable growth conditions or viral infection, but these do not necessarily involve flower reversions. There are many examples of inflorescence reversion but fewer clearly defined cases of flower reversion. In flower reversion the meristem of the flower itself reverts to vegetative growth so that flowers with basal floral organs and distal leaves on the same axis are formed successively by the apical meristem. In Pharbitis nil, Anagallis arvensis, and Impatiens balsamina flower reversions have been caused by defined environmental conditions. However, only in Impatiens has detailed study of the changes in growth and development at the shoot apex during reversion been carried out. These studies show that changes in apical growth and phyllotaxis that typically accompany flowering can be separated from the development of floral organs and suggest that the floral stimulus plays a role throughout flower morphogenesis. The occurrence of reverting organs intermediate between leaves and petals is of particular interest in allowing experiments to be done on the progress of determination at the cell, tissue and organ levels. Reversion indicates that the flowering process must be regarded as a continuum, with physiological stages such as commitment to flower, and even morphological stages such as different floral organ types, being to varying extents artificial. Further study of the regulation of floral morphogenesis, and of the events associated with reversion, may provide important information on the nature of the factors that bring about the onset of flowering itself. © 1990 The New York Botanical Garden.
