The arrangement of leaves on a plant stem. It is determined by the apical meristem of the growing shoot and is specific to each species. The leaves may be inserted up the stem in whorls (whorled phyllotaxy), in pairs (opposite phyllotaxy), or singly at each node. When arranged in pairs, the two leaves arise on opposite sides of the stem and are usually at right angles to the leaf pairs above and below them. Single leaves may be inserted alternately (alternate phyllotaxy) or in a spiral pattern (spiral phyllotaxy) up the stem. The most common arrangement in angiosperms is spiral phyllotaxy, which results in the minimum of shading of leaves by those above them. However, the shading afforded by opposite phyllotaxy may be beneficial where plants are subject to intense sunlight.