Some neotropical Vachellia species (Ant-Acacias) have hollowed out thorns which are inhabited by ants and the ascidiate (hollow, pitcher-like) leaves of Dischidia are frequently used as domiciles by ants. The leaves of some plants, including many in the Rubiaceae such as Coffee, have less pronounced adaptations, merely dimples in the leaf surface which provide a protected area for ants to live.
Species of plants in many families from around the world produce extra-floral nectaries - nectar producing plant parts found outside of the flowers in leaves, stems and twigs. While nectar sources from flowers may be distinctly seasonal in availability, most plants with extra-floral nectaries produce them year-round, thus ensuring the benefits of the symbioses outside of the flowering season. Having extra-floral nectaries may also serve as a distraction from floral nectaries, where ants and other crawling insects could interfere with proper pollination of the flowers. In most cases, harvesting of nectar from extrafloral nectaries is not specific to any one insect group, but ants make very good use of these food sources when available and will often defend such 'prime territory' thus benefiting the plants.
Finally, dispersal of some seeds can be facilitated by the presence of fat containing elaiosomes on the seeds, which encourages ants, as well as other insects, to harvest the seeds and carry them off where, hopefully, some of them will fall by the wayside to serve as propagules for the parent plant.
An excellent article on the cultivation of selected epiphytic ant-plants appeared in the 2000 Cactus and Succulent Journal1
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