It is the mode of arrangement / distribution of leaves on stem or itís branch.
Phyllotxy ensures that leaves may receive maximum sunlight for photosynthesis.
In such case only one leaf is attached at each node. The leaves are so arranged that a line drawn on the stem through the leaf bases will take a spiral course. Ex. Hibiscus, Brassica etc.
In such case two leaves are present at each node, standing opposite to each other. It is of two subtypes -
Here pairs of leaves at each successive node are placed at right angle to each other. Eg. Ocimum, Calotropis etc.
Here pairs of leaves at each successive node are placed over each other in same plane. Eg.Eugenia,Quisqualis etc.
In this type more than two leaves are present at each node, forming a whorl. Ex. Oleander, Alstonia etc.