Individuals of Marsilea quadrifolia, an amphibious fern, experiencing xtreme variations in environment develop heterophyll with different morphological haracteristics. The objective of this study is to investigate if ethylene can induce floating type of leaves in his fern. To achieve this goal, ratio of stomatal density on abaxial and adaxial leaf surfaces (stomatal atio) and the mass per unit length of petiole (PML), on leaves of terrestrial shoots sprayed with an ethylene as releaser, Ethephon, were compared with those of leaves produced by submergence of terrestrial hoots. Leaves with different stomatal ratio and PML, corresponding to that of terrestrial type and loating type of leaves, were produced when terrestrial shoots of M. quadrifolia were submerged. The esult reveals that the plasticity of leaves to respond to submergence depends on leaf’s age. Application of thephon significantly altered the stomatal ratio of young leaves on terrestrial shoot but not their PML. eaves response to Ethephon treatment was also age dependent. These results indicate that ethylene ight be involved in the formation of floating leaves in M. quadrifolia.