•The parasitic plant Cuscuta exchanges diverse macromolecules with its hosts.•Trans-species microRNAs from Cuscuta regulate host genes.•The genes encoding these microRNAs could originate from horizontal-gene transfer events.•Extracellular vesicles are one possible mechanism for how trans-species microRNAs are delivered to the host. Parasitic plants make direct contact with their host’s vasculature. In parasitism by Cuscuta, RNA and other macromolecules regularly move between host and parasite. Recently, trans-species microRNA from Cuscuta have been shown to functionally target host genes which have essential roles in host defense. Known pathways for the evolution of microRNAs, and the prevalence of horizontal gene transfer events in the Cuscuta lineage, hint that trans-species microRNAs could originate from captured host genes. It is unknown how the delivery of microRNAs from the parasite to the host takes place. One exciting possibility is through apoplastic export using extracellular vesicles, a process which has recently been shown to transport select small RNAs in plants and fungi. These discoveries represent the initial findings of what may be a widespread mechanism of interactions between species.