Hint: In different plant species, the arrangement of the leaves on the stems and the branches follows particular patterns. This non-random arrangement of leaves is known as phyllotaxy, and is useful in classification and identification of plants.
There are three types of phyllotaxy: alternate, whorled, and opposite.
In alternate phyllotaxy, individual leaves arise from each node on the stem of the plant, and the arrangement from node to node along the stem is in a spiral pattern. This kind of phyllotaxy is seen in sunflowers, peepul, and mustard plants.
Opposite phyllotaxy, on the other hand, has pairs of leaves arising from each node, as they are arranged on opposite sides of the stem, they have been classified as such. The common plants guava and jamun have opposite phyllotaxy. This is also known as paired phyllotaxy for obvious reasons.
When there are three or more leaves arising from each node, the plant is said to have whorled phyllotaxy. Plants like Nerium and Alstonia have whorled phyllotaxy. When looking down the top of a stem with alternate phyllotaxy, because of the spiral arrangement, the leaves may appear whorled, but they are not arising at the same node. Whorled arrangement is more common on plants that have very short internodes, and leaves can be arranged in rosettes.
Note: Besides the arrangement of the leaves on the stem, plants are also categorised according to leaf shape, venation, margins, and whether they are compound or simple. Leaves may also have different kinds of modifications.