Sexual system variation in legumes (Leguminosae): underpinning genomic study with new tools to describe inflorescence morphology

Although the great majority of legume species are cosexual with hermaphrodite flowers, a variety of sexual systems are observed in the family, including monoecy, andromonoecy, androdioecy and dioecy. Such broad terms conceal much variation, details that may be of importance in understanding the evolutionary and ecological basis of reproductive systems. This variation is often inadequately described in taxonomic works which, through practical necessity, require brevity. Here, we provide a brief overview of the sexual systems of legumes and propose a simple notation for summarizing sexual variation in the form of an unequivocal formula: the inflorescence formula. We also suggest a protocol for the detailed description of sexual variation, which we hope will be useful in guiding future studies of sexual variation in plants. Thorough knowledge of sexual variation at the morphological level is an important prerequisite for molecular investigation of the evolutionary developmental biology of sex systems. Legumes provide a rich field for future evo-devo investigations in this area.