Three of the most common and important structural adaptations of ant plants are extrafloral nectaries, domatia, and (least commonly) Beltian bodies. Plant domatia are formed nesting sites provided by the plant in the form of hollow stems, petioles, thorns, or curled leaves. The production of ant-specialized domatia has been documented in over 100 genera of tropical plants. Beltian bodies provide a high-energy food source to ants in the form of nutritive corpuscles produced on leaflet tips, and they have been described in at least 20 plant families. Extrafloral nectaries (EFNs) are known to occur in at least 66 families of angiosperm plants in both temperate and tropical regions, as well as some ferns, but are absent in all gymnosperms and are most abundant in the tropics. EFNs being outside of the plant flowers are not employed in pollination; their primary purpose is to attract and sustain tending ants. Many plants can control the flow of nectar from the EFNs so that the availability of nectar varies according to daily and seasonal cycles. Because ants can respond quickly to changes in flow rate from EFNs, this may be possible mechanism by which plants can induce greater ant activity during times of peak herbivory, and minimize overall costs of nectar production. The combined nutritional output of EFNs and Beltian bodies can be a significant food source for tending ants, and in some cases can provide the total nutritive needs for an ant colony.