Flowers are borne on reproductive axes, either as solitary structures or on inflorescences, which can be unbranched or variously branched (Figure 5.1). In a determinate inflorescence, the inflorescence apex is terminated by a flower, whereas in an indeterminate inflorescence it maintains growth until the apical meristem becomes exhausted. Each flower is often subtended by one or two modified leaf-like sterile bracts borne on the inflorescence axis, though bracts are entirely absent from some species. Some species also possess one or more leaf-like bracteoles on the flower axis. At the onset of flowering, the shoot apical meristem undergoes structural modification that transforms it from a vegetative apex to a reproductive apex.