Modular growth in seed plants may be analysed in terms of three architectural elements: the unit of morphogenesis, the module and the architectural model. Some of the salient features of these structures are reviewed, compared and contrasted. A variety of plant shapes and sizes may be derived schematically from them by two sorts of transformation, gigantism and repetition. The former is uncommon in seed plants, but repetition produces a wide array of constructions. Repetition of the architectural model, a process known as reiteration, leads to a colonial structure characteristic of the crowns of many mature trees. This is often an expression of the plant's opportunistic response to environmental variations in resource availability. The reiterated complexes formed as a result may show some characteristic ontogenetic and phylogenetic sequences to give an architectural continuum of construction.