heterophylly

Heterophylly is the occurrence of two or more distinct leaf forms on a single plant. It is a form of phenotypic plasticity in which leaf morphology varies within an individual, often between shoots or along the same shoot.

In aquatic and semi-aquatic plants, heterophylly is particularly well documented: submerged leaves are typically narrow, linear, and sometimes dissected to reduce buoyancy and facilitate gas exchange and water flow; aerial or floating leaves are broader and less dissected to maximize light capture at the surface. Some terrestrial species also show heterophylly, with juvenile leaves that differ in shape or size from adult leaves as the plant ages or in response to shading.

Causes include environmental cues such as light quality and intensity, depth of water, humidity, temperature, and nutrient status, as well as developmental stage. The developmental programs appear to be under hormonal control, with regulators such as auxin, ethylene, gibberellins, and abscisic acid implicated in guiding leaf form in response to conditions.

Functionally, heterophylly allows a single plant to optimize photosynthesis, gas exchange, and resource use across heterogeneous environments, enhancing survival and growth when conditions change. See also: phenotypic plasticity; heteroblasty.