A parasitic plant is one that derives some or all of its nutritional requirements from another living plant. All parasitic plants have modified roots, named haustoria (singular: haustorium), which penetrate the host plants, connecting them to the conductive system - either the xylem, the phloem, or both. This provides them with the ability to extract water and nutrient from the hosts. About 4,100 species in approximately 19 families of flowering plants are known.