Domatia

Domatia (singular: domatium) are small cavities, pockets or tufts of hair usually found in the axils of veins on the lower surface of leaves. They are often linked to the presence of ants or mites. Domatia are sometimes difficult to distinguish from glands.

Use a hand lens or microscope to look for this feature.

Examples from neotropical taxa:

Enriquebeltrania crenatifolia (Euphorbiaceae)

Adelia barbinervis (Euphorbiaceae)