Branching in stems with (diagram)


A plant’s below- or above-ground stems or shoots often exhibit characteristic branching patterns. The relative activity of apical meristems determines the branching pattern; the original shoot apical meristem is derived from the seedling epicotyl, and apical meristems are subsequently derived from lateral buds.

One major feature of the branching pattern is the duration of a shoot’s apical meristematic growth. If a given shoot has the potential for unlimited growth, such that the apical meristem is continuously active, the growth is termed indeterminate.

If, instead, a shoot terminates growth after some time, with either the abortion of the apical meristem or its conversion into a flower, inflorescence or specialized structure (such as a thorn or tendril), the growth is termed determinate. (Note that these same terms are used for inflorescence development; see later discussion.)

Two other related terms have to do with flowering. A determinate shoot that completely transforms into a flower or inflorescence is called hapaxanthic. An indeterminate shoot that bears lateral flowers but continues vegetative growth is pleonastic.

Many different models of stem branching patterns have been described (e.g., see HallØ et al. 1978). These models may be of taxonomic value and are interesting from a bio-mechanical perspective, as they may represent evolutionary adaptations to a given environment or life strategy.

Monopodial Branching

Three general terms focus on a branch or axis’s developmental origin. If a given stem axis is derived from the growth of a single apical meristem, the pattern is termed monopodial. The monopodial axis may grow indefinitely and thus be indeterminate.

Sympodial Branching

In contrast, if a given axis (which may appear to be a single, continuous structure) comprises numerous units derived from separate apical meristems, the branching pattern is sympodial. These sympodial units arise from lateral buds that are proximal to the apical meristem of the original shoot.

Many rhizomes have sympodial growth. Finally, a rare type of branching is dichotomous, in which a single apical meristem divides equally into branches, e.g., Psilotum.

Figure. Stem branching patterns.
Figure. Stem branching patterns.

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