Define phyllotaxy. Mention its types.

Explanation

The mode of arrangement of leaves on the stem is known as phyllotaxy (Greek. Phyllon=leaf taxis =arrangement), Phyllotaxy is to avoid over crowding of leaves and expose the leaves maximum to the sunlight for photosynthesis. The four main types of phyllotaxy are:
1. Alternate 2. Opposite 3. Ternate and 4. Whorled.
1. Alternate phyllotaxy: In this type there is only one leaf per node and the leaves on the successive nodes are arranged alternate to each other. Spiral arrangement of leaves show vertical rows are called orhostichies. They are two types:
(a) Alternate spiral: In which the leaves are arranged alternatively in a spiral manner.
e.g., Hibiscus and Ficus.
(b)Alternate distichous or Bicurious: In which the leaves are organized alternatively in two rows on either side of the stem. eg. Monoon longifolium (Polyalthia longifolia).
2.Opposite phyllotaxy: In this type cach node possess two leaves opposite to each other.
They are organized in two different types:
(i) Opposite superposed: The pair of leaves arranged in succession are in the same direction, that is two opposite leaves at a node is exactly above those at the lower node. e.g., Psidium (Guava), Eugenia jambolana (Jamun) and Quisqualis (Rangoon creeper).
(ii) Opposite decussate: In this type of phyllotaxy one pair of leaves is placed at right angles to the next upper or lower pair of leaves. e.g. Calotropis, Zinnia and Ocimum
3.Ternate phyllotaxy : In this type there are three leaves attached at each node. e.g. Nerium.
4.Whorled (verticillate ) type of phyllotaxy : In this type more than three leaves are present in a whorled at each node forming a circle or wheel. e.g. Allamanda and Alstonia scholaris.