Intersex inflorescences of Rumex acetosa demonstrate that sex determination is unique to each flower

A triploid intersex individual of the normally dioecious species Rumex acetosa showed extreme variability in gynoecium development. Analysis of the development and distribution of these flowers on inflorescences enabled insight to be gained into the mechanism of sex determination. Floral phenotypes on intersex inflorescences were classified according to gynoecium development. Flower morphology was investigated by scanning electron and light microscopy. Organ identity gene expression in intersex floral primordia was assessed using in situ hybridization. The distribution of the different floral phenotypes shows that each individual flower is determined separately, and that the phenotype of each flower is not influenced by its position on the inflorescence, or by the phenotype of neighbouring flowers. C-function gene expression persisted in gynoecia that had ceased development. Gynoecium development in mutant flowers resembled the phenotype of the Arabidopsis mutant ettin and suggests that a hormone gradient may be involved. C-function expression does not appear to control the extent of female development, and indicates that genes which are downstream of the organ-identity genes must control organ suppression.