Haustorien

Haustorien is the plural form of haustorium, a botanical and mycological term for a specialized feeding structure formed by certain parasitic fungi, oomycetes, and parasitic plants. Haustoria enable the parasite to connect with the host’s tissues and extract water, ions, sugars, and other nutrients necessary for growth. In English usage, the plural haustoria is common, while in German contexts the term Haustorien is used.

In fungi and oomycetes, haustoria develop at the interface with the host and typically invade host tissue. A haustorial hypha grows into or between host cells and forms an enlarged tip that invaginates the host plasma membrane. Nutrients pass from the host into the extrahaustorial space and then into the fungal or oomycete cytoplasm across the haustorial membrane. This specialized interface helps the pathogen obtain resources while often avoiding complete host cell destruction. Haustoria are characteristic of many rusts, downy mildews, and other obligate biotrophs, and they play a central role in disease development and host specificity.

Parasitic plants such as Cuscuta (dodders) and Orobanche (broomrapes) also form haustoria. In these plants, haustoria penetrate host tissues to access vascular systems, allowing transfer of water and nutrients. They can be intracellular or extracellular relative to host cells, and their formation is influenced by chemical signals from the host.

Ecological and agricultural relevance is high, as haustoria underpin the success of many pathogens and parasites. Plant defenses often target haustorial formation or function to limit infection. Understanding haustoria informs disease management and plant–pathogen coevolution studies.