Anisophylly
Anisophylly is when leaves of a pair differ from one another, either in size or in shape. When a horizontal stem also exhibits anisophylly, the photosynthetic leaf surfaces interfere less with light from above, and rotation of the leaf or the petiole can enhance that effect. The phenomenon is relatively common in some tropical plant families with decussate leaf arrangement, such as Melastomataceae, Gesneriaceae and Urticaceae as well as in certain species of other families.