Phenotypic plasticity of sylleptic branching: Genetic design of tree architecture

The crown of many trees is composed of a main axis and branches. All branches arise from axillary or lateral buds and two types of branches exist: proleptic and sylleptic. Proleptic branches form from buds that have undergone a rest period, typically associated with winter dormancy, whereas sylleptic branches emerge without a rest and without complete bud formation. All trees have proleptic branches; some trees with the indeterminant growth habit have both proleptic and sylleptic branches. Sylleptic branches may play an important role in determining tree growth, architecture and adaptation for many temperate-zone woody plants. We review evidence for the phenotypic plasticity of sylleptic branches and its genetic, environmental, and developmental control.