haustorium

Haustorium (plural haustoria) is a specialized organ used by some parasitic plants and parasitic fungi to draw water, minerals, and other nutrients from a host. The term comes from Latin haustorium, from haurire "to draw up." In plants, haustoria arise from the organ of the parasite (often a root or stem) after contact with a host. They penetrate the host’s outer tissues and reach the vascular system, connecting with xylem and/or phloem. The haustorium may include intrusive cells that breach host tissues and transfer cells that facilitate nutrient exchange. Depending on the parasite, haustoria may be externally located on the host surface (ectotrophic) or embedded within host tissue (endotrophic). Parasitic plants such as Cuscuta (dodder), Orobanche, and Striga form haustoria to withdraw water and minerals; some also obtain fixed carbon from the host.

In fungi, haustoria are specialized hyphal structures formed by biotrophic plant pathogens such as rusts (Puccinia, Melampsora) and powdery mildews. These haustoria invaginate the host cell plasma membrane, creating a tight interface known as the haustorial complex, and absorb nutrients without killing the host cell. They are often accompanied by an extrahaustorial membrane and delimiting host responses.

Haustoria are a key adaptation for parasitism, influencing host range and disease dynamics. They are studied in agronomy due to their role in crop losses and in plant pathology as a model of host–parasite interfaces.