1. The arrangement of leaves on the stem or the branches in known as phyllotaxy. (Gk. Phyllon = leaf, taxis = arrangement).
2. Phyllotaxy is to avoid over crowding of leaves so as to expose the leaves to maximum sunlight for photosynthesis.
3. The four main types ofphyllotaxy are Alternate, Opposite, Ternate, Whorled.
Alternate phyllotaxy:
In this type there is only one leaf per node and leaves on the successive nodes are arranged alternate to each other. Spiral arrangement of leaves show vertical rows are called orthostichies. They are two types.
(a) Alternate spiral: In which the leaves are arranged alternatively in a spiral manner. Eg: Hibiscus.
(b) Alternate distichous or Bifarious: In which the leaves are organized Superposed - Guava alternatively in two rows on either side of the stem. Eg: Polyalthia.
Opposite phyllotaxy :
Each node possess two leaves opposite to each other. They are organized in two different types.
(a) Opposite superposed: The pair of leaves arranged in succession are in the same direction that is two opposite leaves at a node lie exactly above those at the lower node. Eg: Psidium.
(b) Opposite decussate: One pair of leaves is placed at right angles to the next upper or lower pair of leaves. Eg: Calotropis.
Ternate phyllotaxy :
There are three leaves attached at each node. Eg: Nerium.
Whorled (verticillate) type of phyllotaxy :
More than three leaves are present Temate -Nerium in a whorl at each node forming a circle or whorl.
Eg: Allamanda.
