
Myrmecophytes (; literally "ant-plant") are plants that live in a
mutualistic association with a colony of ants. There are over 100 different genera of myrmecophytes.
These plants possess structural adaptations in the form of
domatia
A domatium (plural: domatia, from the Latin "domus", meaning home) is a tiny chamber that houses arthropods, produced by a plant.
Ideally domatia differ from galls in that they are produced by the plant rather than being induced by their inhabi ...
where ants can shelter, and food bodies and extrafloral nectaries that provide ants with food.
In exchange for these resources, ants aid the myrmecophyte in pollination, seed dispersal, gathering of essential nutrients, and defense.
Domatia adapted specifically to ants may be called myrmecodomatia.
Mutualism

Myrmecophytes share a
mutualistic relationship with ants, benefiting both the plants and ants. This association may be either facultative or obligate.
Obligate
In obligate mutualisms, the organisms involved are interdependent; they cannot survive on their own. An example of this type of mutualism can be found in the plant genus ''
Macaranga
''Macaranga'' is a large genus of Old World tropical trees of the family Euphorbiaceae and the only genus in the subtribe Macaranginae (tribe Acalypheae). Native to Africa, Australasia, Asia and various islands of the Indian and Pacific Oc ...
''. All species of this genus provide food for ants in various forms, but only the obligate species produce
domatia
A domatium (plural: domatia, from the Latin "domus", meaning home) is a tiny chamber that houses arthropods, produced by a plant.
Ideally domatia differ from galls in that they are produced by the plant rather than being induced by their inhabi ...
.
Some of the most common species of myrmecophytic ''Macaranga'' interact with ants in the genus ''
Crematogaster
''Crematogaster'' is an ecologically diverse genus of ants found worldwide, which are characterised by a distinctive heart-shaped gaster (insect anatomy), gaster (abdomen), which gives them one of their common names, the Saint Valentine ant. Mem ...
''. ''C. borneensis'' have been found to be completely dependent on its partner plant, not being able to survive without the provided nesting spaces and food bodies. In laboratory tests, the worker ants did not survive away from the plants, and in their natural habitat they were never found anywhere else.
Facultative
In facultative mutualism, the survival of the parties (plant and ants, in this instance) does not depend upon the interaction. Facultative mutualisms most often occur in plants that have extrafloral nectaries but no other specialized structures for the ants.
These non-exclusive nectaries allow a variety of animal species to interact with the plant.
Facultative relationships can also develop between non-native plant and ant species, where
co-evolution
In biology, coevolution occurs when two or more species reciprocally affect each other's evolution through the process of natural selection. The term sometimes is used for two traits in the same species affecting each other's evolution, as well a ...
has not occurred. For example, Old World legumes that were introduced to North America can be protected by ants that originated from the plants' regions of origin.
Structural adaptations
Domatia

Domatia are internal plant structures that appear to be specifically adapted for habitation by ants.
These cavities are found primarily in the stems, leaves, and spines of plants. Many different genera of plants offer domatia. Plants of the genus ''
Acacia
''Acacia'', commonly known as wattles or acacias, is a genus of about of shrubs and trees in the subfamily Mimosoideae of the pea family Fabaceae. Initially, it comprised a group of plant species native to Africa, South America, and Austral ...
'' have some of the most widely recognized forms of domatia and offer some of the best examples of ant-plant obligate mutualism.
Different ''Acacia'' species provide a variety of resources needed for their codependent counterparts. One of these resources is the need for shelter. ''Acacia'' have enlarged thorns on their stems that are excavated by ants for use as housing structures.
Since the tree contains their nest, these aggressive ants react strongly to any disturbance of the tree, providing the myrmecophyte with defense from grazing herbivores and encroaching vines.
Domatia can also be found within the tubers of certain plants.
Tubers form when the
hypocotyl
The hypocotyl (short for "hypocotyledonous stem", meaning "below seed leaf") is the stem of a germinating seedling, found below the cotyledons (seed leaves) and above the radicle (root).
Eudicots
As the plant embryo grows at germination, it send ...
s of a seedling swells to form a hollow, chambered structure that can become inhabited by ants.
The plant family
Rubiaceae
Rubiaceae () is a family (biology), family of flowering plants, commonly known as the coffee, madder, or bedstraw family. It consists of terrestrial trees, shrubs, lianas, or herbs that are recognizable by simple, opposite leaves with Petiole ( ...
contains the most commonly known tuberous myrmecophyte, ''
Myrmecodia
''Myrmecodia'' is a genus of Epiphyte, epiphytic plants, present in Indochina, Malesia, Papuasia, and Queensland, Australia. It is one of five ant-plant genera in the family Rubiaceae, the others being ''Anthorrhiza'', ''Hydnophytum'', ''Myrme ...
''.
Food bodies

Some plants produce food bodies for use by other organisms. These small
epidermal
The epidermis is the outermost of the three layers that comprise the skin, the inner layers being the dermis and hypodermis. The epidermal layer provides a barrier to infection from environmental pathogens and regulates the amount of water relea ...
structures contain a variety of nutrients that are removed and consumed by foragers.
Food bodies are identified by the main nutrient they contain and by the genus of plant producing them.
Beltian bodies
A Beltian body is a detachable tip found on the pinnules of some species of ''Acacia'' and closely related genera. Beltian bodies, named after Thomas Belt, are rich in lipids, sugars and proteins and often red in colour. They are believed to have ...
are found on the leaflet tips of ''Acacia'' plants and have relatively high protein content. Beccarian bodies are found on young leaves of the genus ''
Macaranga
''Macaranga'' is a large genus of Old World tropical trees of the family Euphorbiaceae and the only genus in the subtribe Macaranginae (tribe Acalypheae). Native to Africa, Australasia, Asia and various islands of the Indian and Pacific Oc ...
'' and are especially rich in
lipids
Lipids are a broad group of organic compounds which include fats, waxes, sterols, fat-soluble vitamins (such as vitamins Vitamin A, A, Vitamin D, D, Vitamin E, E and Vitamin K, K), monoglycerides, diglycerides, phospholipids, and others. The fu ...
. Lipids are also the main nutrient found in
pearl bodies
Pearl bodies are small (0.5 - 3.0 mm), lustrous, pearl-like food bodies produced from the epidermis of leaves, petioles and shoots of certain plants. They are rich in lipids, proteins and carbohydrates, and are sought after by various arthrop ...
, found on the leaves and stems of ''Ochroma'' plants. Most ant inhabitants of ''
Cecropia
''Cecropia'' is a Neotropical genus consisting of 61 recognized species with a highly distinctive lineage of dioecious trees.
The genus consists of pioneer trees in the more or less humid parts of the Neotropics, with the majority of the speci ...
'' plants harvest
Müllerian bodies, as their primary food source. Remarkably these Müllerian bodies, found on the stalk of the leaf, are primarily
glycogen
Glycogen is a multibranched polysaccharide of glucose that serves as a form of energy storage in animals, fungi, and bacteria. It is the main storage form of glucose in the human body.
Glycogen functions as one of three regularly used forms ...
. Glycogen is the principal storage
carbohydrate
A carbohydrate () is a biomolecule composed of carbon (C), hydrogen (H), and oxygen (O) atoms. The typical hydrogen-to-oxygen atomic ratio is 2:1, analogous to that of water, and is represented by the empirical formula (where ''m'' and ''n'' ...
found in
animal
Animals are multicellular, eukaryotic organisms in the Biology, biological Kingdom (biology), kingdom Animalia (). With few exceptions, animals heterotroph, consume organic material, Cellular respiration#Aerobic respiration, breathe oxygen, ...
s and is extremely rare in plants.
Extrafloral nectaries

Extrafloral nectaries are sugar-producing glands found outside the flower structures of plants. They occur in many different plant species around the world and are most commonly associated with vegetative structures that normally do not have nectaries, such as leaves, stems, and twigs.
These secreting structures are often non-exclusive in that nectar can be taken by a variety of animals; however, in some obligate myrmecophyte plants such as ''
Acacia collinsii
''Vachellia collinsii'', previously ''Acacia collinsii'', is a species of flowering plant native to Central America and parts of Africa.
Distribution
''Vachellia collinsii'' is native to Central America and parts of Africa. In southern Centra ...
'', extrafloral nectar is modified to be attractive only to the ant partners in the symbiosis.
The nectar thus provided feeds ants, which in turn protect these myrmecophytes from herbivorous activity. A species of deciduous tree that displays extrafloral nectaries, ''
Catalpa speciosa
''Catalpa speciosa'', commonly known as the northern catalpa, hardy catalpa, western catalpa, cigar tree or catawba, is a species of ''Catalpa'' native to the midwestern United States.
The Latin specific epithet ''speciosa'' means "showy".
Desc ...
'', shows a decreased loss of leaf tissue on branches protected by ants, and an increase in number of seeds produced.
Ant-plant interactions
Ants as pollinators
Unlike their bee relatives, ants rarely pollinate plants. Various suggestions have been made as to why ants are poor pollinators, although none have been verified: a) ants do not fly, limiting their transport of pollen far enough to effect
cross-pollination
Xenogamy (Greek ''xenos''=stranger, ''gamos''=marriage) is the transfer of pollen grains from the anther to the stigma of a different plant. This is the only type of cross pollination which during pollination brings genetically different types of ...
, b) ants do not systematically forage as bees do, and c) ants are not hairy, and clean themselves too frequently to allow pollen to be carried to other plants.
In most cases of ant pollination, the ants are one of multiple pollinators, meaning that the plants are not completely dependent on ants for pollination. However, the orchid ''
Leporella fimbriata
''Leporella fimbriata'', commonly known as ''hare orchid'' or ''fringed hare orchid'', is the only species in the flowering plant genus ''Leporella'' in the orchid family, Orchidaceae and is endemic to the southern Australia mainland. It is rela ...
'' can only be pollinated by its winged male ant partner (''
Myrmecia urens
''Myrmecia urens'' is a species of ant in the genus ''Myrmecia'' (bulldog ants) found in Australia.
Taxonomy
Behaviour and ecology
While pollination by ants is somewhat rare, the orchid ''Leporella fimbriata'' is a myrmecophyte
Myrmecophyt ...
'').
Ants and seed dispersal
Myrmecochory
Myrmecochory ( (sometimes myrmechory); from ("ant") and ''khoreíā'' ("circular dance") is seed dispersal by ants, an ecologically significant Myrmecophily, ant–plant Biological interaction, interaction with worldwide distribution. Most ...
, "ant-dispersal," is the collection and dispersal of seeds by ants. Ants disperse more than 30% of the spring-flowering herbaceous plants in eastern North America.
Both the plant and the ant benefit in this scenario. The ants are provided with an
elaiosome
Elaiosomes ( ''élaion'' "oil" + ''sóma'' "body") are fleshy structures that are attached to the seeds of many plant species. The elaiosome is rich in lipids and proteins, and may be variously shaped. Many plants have elaiosomes that attract ...
, a detachable food body found on the surface of the seed. Elaiosomes have diverse compositions, usually high in
lipids
Lipids are a broad group of organic compounds which include fats, waxes, sterols, fat-soluble vitamins (such as vitamins Vitamin A, A, Vitamin D, D, Vitamin E, E and Vitamin K, K), monoglycerides, diglycerides, phospholipids, and others. The fu ...
and
fatty acids
In chemistry, in particular in biochemistry, a fatty acid is a carboxylic acid with an aliphatic chain, which is either saturated or unsaturated. Most naturally occurring fatty acids have an unbranched chain of an even number of carbon atoms, ...
, but also containing
amino acids
Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although over 500 amino acids exist in nature, by far the most important are the Proteinogenic amino acid, 22 α-amino acids incorporated into p ...
, sugars, and protein.
The ants remove the elaiosome once the seed has been transported to the colony. As a result, the seeds are safely placed in nutrient-rich substrate protected from
predator
Predation is a biological interaction in which one organism, the predator, kills and eats another organism, its prey. It is one of a family of common List of feeding behaviours, feeding behaviours that includes parasitism and micropredation ...
s, benefiting the plant with optimum establishment conditions for its seed.
Ants feeding plants
Myrmecotrophy, meaning "ant-fed," is the ability of plants to absorb nutrients from debris piles left by ant nests or, in the case of ''
Nepenthes bicalcarata
''Nepenthes bicalcarata'' (; from Latin
Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now ...
'', from ant
egesta. The tropical tree ''
Cecropia peltata
''Cecropia peltata'' is a fast-growing tree in the genus ''Cecropia''. Common names include trumpet tree, trumpet-bush, bacano, bois canon and snakewood. It is listed as one of the List of the world's 100 worst invasive species, world's 100 worst ...
'' obtains 98% of its nitrogen from the waste deposited by its ant counterparts.
A 2014 study by Chanam et al. showed how domatia could evolve without a specialised protection-based symbiosis. Nutritional benefits can be provided by multiple species of ant (including protective, non-protective and even plant-damaging species) and other invertebrates. The myrmecophyte ''
Humboldtia brunonis
''Humboldtia'' is a genus of flowering plants in the family Fabaceae. It includes eight species of trees and shrubs native to India and Sri Lanka. Most species are endemic to the Western Ghats of southwestern India
India, officially t ...
'' sometimes bears domatia, whereas all individuals produce extrafloral nectar. Domatia-bearing ''H. brunonis'' plants have greater fruit set and hence greater reproductive success, than those without domatia. Plant tissues near domatia received additional nitrogen compounds from the harboured species.
Ants as defense

Since plants provide essential resources for ants, the need to protect the plant and those resources is extremely important. Many myrmecophytes are defended from both herbivores and other competing plants by their ant symbionts.
''
Acacia cornigera
''Vachellia cornigera'', commonly known as bullhorn acacia (family (biology), family Fabaceae), is a swollen-thorn tree and myrmecophyte native to Mexico and Central America. The common name of "bullhorn" refers to the enlarged, hollowed-out, swo ...
'', for example, is thoroughly guarded by its obligate ant partner, ''
Pseudomyrmex ferruginea
The acacia ant (''Pseudomyrmex ferruginea'') is a species of ant of the genus ''Pseudomyrmex''. These arboreal, wasp-like ants have an orange-brown body around 3 mm in length and very large eyes. The acacia ant is best known and named for ...
''. A single colony of ''P. ferruginea'' may contain more than 30,000 ants, and can tend multiple ''Acacia'' trees.
The soldier ants are extremely aggressive, patrolling the trees twenty-four hours a day. Any disturbance to the tree alerts ants, who then recruit more workers from inside the horn domatia. These ants defend the ''Acacia'' by biting, violently stinging, and pruning any trespassers. The ants keep the plant free from other insects, vertebrate herbivores, invading fungi, and other plants.
See also
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Ant garden
An ant garden is a Mutualism (biology), mutualistic interaction between certain species of arboreal ants and various Epiphyte, epiphytic plants. It is a structure made in the tree Canopy (biology), canopy by the ants that is filled with debris and ...
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List of symbiotic relationships
References
Sources
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{{refend
Myrmecophytes
Myrmecophytes (; literally "ant-plant") are plants that live in a Mutualism (biology), mutualistic association with a colony of ants. There are over 100 different genera of myrmecophytes. These plants possess structural adaptations in the form o ...
Ants
Mutualism (biology)
Botany
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