Types of Phyllotaxis

In the mid-1830s naturalists noticed the spirals in the capituli of daisies and sunflowers. There are indeed two easily recognizable families of spirals, winding in opposite directions with respect to a common pole that is the center of the capitulum. They also noticed the patterns of scales making families of spirals on the pineapple fruit surface. Depending on whether the scales are rectangular or hexagonal, there are two or three such families of spirals or helices that can be easily observed. These spirals are referred to as parastichies, meaning "secondary spirals." The accompanying figure of the Pinus pinea shows a cross-section of an apical bud with five parastichies in one direction and eight in the opposite direction. Similar patterns of helices are made by the points of insertions of the leaves around stems, such as the patterns of scars made by the leaves on the trunk of a palm tree.

Apart from the spiral or helical pattern, which is the type most frequently encountered in nature, there is another main type of phyllotaxis called whorled. A pattern is whorled when n primordia appear at each level of the stem, such as in horsetails (Equisetum), in which n can take values from 6 to 20. When the n primordia on a level are inserted in between those of the adjacent level, the whorl is said to be alternating, as in fir club moss (Lycopodium selago). When they are directly above those in the adjacent level, the whorl is called superposed, as in Ruta and Primula.

Cross-section of an apical bud of Pinus pinea, with five parastichies in one direction and eight in the opposite direction.

capitulum the head of a compound flower, such as a dandelion vascular related to transport of nutrients apical at the tip

whorl a ring

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