Significance In many plants, flowering is regulated by environmental cues, such as day length. Under flowering-inductive conditions, leaves synthesize and transmit FLOWERING LOCUS T (FT) protein to the shoot apex, where FT activates flowering. Dodder Cuscuta australis , which is a root- and leafless parasitic plant, however, very likely does not have fully functional FT genes, and it flowers only when the host plants flower. We show that host-synthesized FT protein is able to move into dodder stems, where FT physically interacts with dodder FD transcription factor, activating flowering of dodder. This specific manner of flowering allows dodder to synchronize its flowering time with that of the host plant, and this is likely a trait that is beneficial for dodder’s reproductive success.