Notice the difference in leaf arrangement in plants

If you closely examine, you can see that the leaves in different plants are arranged in different manner. Leaves may be either ALTERNATE, in which the leaves alternate in the twig. In some other plants, the leaves are OPPOSITE. They emerge in pairs, opposite of one another from the twig. The arrangement of leaves in the plant stem is know as Phyllotaxy. By studying phyllotaxy, one can differentiate between different plant species.