The developmental architecture of Isertia coccinea Vahl. (Rubiaceae) is described in terms of modular construction. In this paper a module is defined as a determinate shoot terminating in an inflorescence. Isertia coccinea Vahl. is a small tree that conforms to Scarrone's architectural model. Before flowering, this tree is not modular and consists of an orthotropic trunk bearing rhythmic tiers of orthotropic branches. In a later stage, the lateral complexes branch sympodially as a result of terminal flowering, the whole tree displaying a partly modular stage. Later still, the trunk can terminate in an inflorescence, the tree's growth thus becoming entirely modular. The partly modular stage can be of long or short duration depending on the environmental conditions. In shaded conditions, this stage is long or indeterminate; in open conditions it can be very short, the entirely modular stage becoming dominant early in the life of the tree.