To elucidate the factors which control the flower phenotypic plasticity of Catasetum fimbriatum, studies focusing the floral development of the species were performed. The treatments were: high light intensity (1613 μmol.m-2.s-1); low light intensity (454 μmol.m-2.s-1) and mean light intensity (827 μmol.m-2.s-1). The floral morphology and anatomy were analyzed to evaluate of the sequence of tissue development involved in the sexual differentiation. We found the presence of cell cluster with meristematic features in the ovaries and gynostemium of the male and female diclinous flowers. These are responsible for the definition of the sexual expression of the species, in the dependence of the environmental stimulus, related to the endogenous concentration of ethylene, allowing, consequently, the dedifferentiation and re-differentiation of those clusters in the sexual determination of the flowers. There were no anatomical differences in floral tissues in different treatments. 

Palabras clave: Orchid, sexual expression, anatomy