Leaf symmetry

Leaf symmetry

1.  Dorsiventral leaf

When the leaf is flat, with the blade placed horizontally, showing a distinct upper surface and a lower surface, as in most dicotyledons, it is said to be dorsiventral. Example: Tridax.

2.  Isobilateral leaf

When the leaf is directed vertically upwards, as in many monocotyledons, it is said to be isobilateral leaf. Example: Grass.

3.  Centric leaf

When the leaf is more or less cylindrical and directed upwards or downwards, as in pine, onion, etc., the leaf is said to be centric.

4.  Heterophylly

Occurrence of two different kinds of leaves in the same plant is called heterophylly. Heterophylly is found in many aquatic plants. Here, the floating or aerial leaves and the submerged leaves are of different kinds. The former are generally broad, often fully expanded, and undivided or merely lobed, while the latter are narrow, ribbon-shaped, linear or much dissected. Heterophylly in water plants is, thus, an adaptation to two different conditions of the environment. Example: water crowfoot (Ranunculus aquatilis), water plantain (Alisma plantago), arrowhead (Sagittaria), Limnophila heterophylla.

Terrestrial (land) plants also exhibit this phenomenon. Among them Sterculia villosa, jack (in early stages), Ficus heterophylla show leaves varying from entire to variously lobed structures during different developmental stages. Young leaves are usually lobed or dissected and the mature leaves are entire. Such type is known as developmental heterophylly. Example: Eucalyptus, Artocarpus heterophyllus.