Domatium

A domatium (plural: domatia) is a small chamber or modified plant structure produced by a plant that houses arthropods. The arthropods, often ants or mites, provide a benefit to the plant in return for shelter. This symbiotic relationship is a form of mutualism. Domatia are distinct from galls, which are abnormal plant growths caused by parasites or pathogens. Unlike galls, domatia are a normal, pre-programmed part of the plant's morphology.

Domatia come in a variety of forms, including:

• Pockets: Small pouches or depressions on the undersides of leaves, at the junctions of veins.
• Hair tufts: Dense clusters of hairs, often located in vein axils.
• Stem swellings: Enlarged or hollowed-out sections of stems.
• Modified stipules: Enlarged or otherwise modified leaf appendages at the base of the petiole.

The arthropods that inhabit domatia, known as domatia-inhabiting fauna, often defend the plant against herbivores or fungal pathogens. In the case of ants, this defense can be quite aggressive. Mites, on the other hand, may feed on small herbivores or fungal spores. The specificity of the relationship between a plant and its domatia-inhabiting fauna can vary; some plants host a wide range of arthropods, while others have very specific symbiotic partners. The presence and type of domatia can be useful characteristics for plant identification and systematic studies.