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Phyllotaxis or phyllotaxy is the arrangement of leaves on a plant stem. Which originates from a Greek word phýllon "leaf" and taxis "arrangement".
The basic arrangements of leaves on a stem are opposite, or alternate = spiral. Leaves may also be whorled if several leaves arise, or appear to arise, from the same level (at the same node) on a stem. This arrangement is fairly unusual on plants except for those with particularly short internodes.
With an opposite leaf arrangement, two leaves arise from the stem at the same level (at the same node), on opposite sides of the stem. An opposite leaf pair can be thought of as a whorl of two leaves. In an opposite pattern, if successive leaf pairs are perpendicular, this is called decussate.
With an alternate (spiral) pattern, each leaf arises at a different point (node) on the stem.Distichous phyllotaxis, also called "two-ranked leaf arrangement" is a special case of either opposite or alternate leaf arrangement where the leaves on a stem are arranged in two vertical columns on opposite sides of the stem. Examples include various bulbous plants such as Boophone, Aloe seedlings, and also mature Aloe plicatilis.
A whorl can occur as a basal structure where all the leaves are attached at the base of the shoot and the internodes are small or nonexistent. A basal whorl with a large number of leaves spread out in a circle is called a rosette. Example: Alstonia.
Try observing phyllotaxy of plants in and around your vicinity. And name few of them.
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