The classification reveals a pattern in the confusing multitude of tree crops; its usefulness is enhanced because of similarities in ecology and fruitfulness of the species within a class. The contrast between the fruitful, continuously growing single-stemmed species and the rather unfruitful, rhythmically growing branched species is striking. The ecology and husbandry of the two sub-classes of single-stemmed species and their effect on fruitfulness can be described in simple terms, since fruiting is closely linked with growth. The branched species form a large and diverse class. The relationships between branching and rhythmic growth and between branching and floral differentiation are briefly considered. It is concluded that fruitfulness in single-stemmed plants improves with the growth rate, but in branched trees a balance has to be struck between growth and fruiting: moreover in the latter specific stimuli are usually needed to trigger flower initiation and/or bloom. This leads to a different set of research priorities for the two classes of crops. In virtually all branched tree crops grown for their fruit, vegetative growth and sexual differentiation are separated to some extent, either spatially or temporally. Spatial separation finds expression in cauliflory and shoot dimorphism; some characteristics of the species in these two categories are given. Temporal separation is effected through asynchronous or synchronous growth rhythms; sexual differentiation takes place during a quiescent phase in shoot growth. As the growth rhythm changes with tree age and degree of synchrony depends on the climate, further classification of this large category is difficult, the more so since far too little is known about the growth rhythm of most species. Concerted efforts to describe the phenology of these species are strongly recommended.
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