Q.Define phyllotaxy.

Phyllotaxy (Greek phyllon = leaf, taxis = arrangement) is the pattern in which leaves are arranged on the stem, and it functions to avoid overcrowding while exposing the maximum leaf area to sunlight for photosynthesis. There are four main types. In alternate phyllotaxy each node bears a single leaf, with successive leaves alternating up the stem; if the leaves spiral around the stem it is alternate spiral (Hibiscus, Ficus), and if they lie in just two rows on opposite sides of the stem it is alternate distichous/bifarious (Polyalthia longifolia). In opposite phyllotaxy each node bears two leaves facing each other; if successive pairs lie directly above one another it is opposite superposed (Guava, Quisqualis), and if each pair is set at right angles to the pair above and below it, it is opposite decussate (Calotropis, Ocimum). In ternate phyllotaxy three leaves are attached at each node (Nerium). In whorled (verticillate) phyllotaxy more than three leaves radiate from each node in a circle or whorl (Allamanda, Alstonia scholaris).