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the axial organ of a plant (root or stem), consisting of successive secondary axes and arising as a result of topping during growth and branching.
With dichotomous branching, which characterizes lower plants and a number of higher sporebearing plants (for example club mosses), the sympodium arises as a result of the more intensive growth of one of the bifurcated branches and the sideward displacement of the branch at each of the repeated stages of branching. In lateral branching, which is a feature of most higher plants (including all flowering plants), the sympodium forms as a result of the cessation of top growth of the root or the shoot; a lateral root or shoot arises that generally grows in the same direction as the displaced element. Curtailment of activity at the tip of the meristem can be caused by death resulting from external damage (desiccation, freezing, cutting), by the formation of an apical flower or inflorescence that includes the entire tip of the meristem, or by the deflection of the main axis away from the original growth direction.
The trunks and large branches of most hardwood trees and shrubs are typical sympodia, as are the rhizomes of most perennial herbs. Topping occurs in these organs many times, sometimes as often as once a year. Inflorescences that are formed according to the same principle as sympodia are called cymose. The sympodium is most clearly seen in monochasia.
T. I. SEREBRIAKOVA