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A model relating overlapping regulatory functions to floral organ identities. B- and C-function activity contributes to male organ identity, whereas C activity without B contributes to female identity, with additional partners required. Its simple domains are not universal across all angiosperms.

Floral organ identity is the developmental identity of a floral structure, such as a sepal, petal, stamen or carpel. It concerns what kind of organ develops, not merely its position or final size. The ABC model of flower development describes identities through combinations of regulatory functions in overlapping domains.

Genetic perturbation tests these assignments. Loss of the relevant SEPALLATA functions in Arabidopsis thaliana disrupted the normal B- and C-function specification of floral organs, showing that the simple letter combinations require additional molecular partners. ^[ref] An organ appearing in another position and an organ changing its developmental identity are different outcomes. Organ shape alone also need not reveal which regulatory interaction changed.

A botanist who investigated how SEPALLATA genes contribute to floral organ identity, testing how combinations of regulators specify structure.^[ref]