Myrmecophytes (; literally "ant-plant") are

plants Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae exclude ...

that live in a mutualistic association with a colony of ants. There are over 100 different genera of myrmecophytes. These plants possess structural adaptations that provide ants with food and/or shelter. These specialized structures include domatia, food bodies, and

extrafloral nectaries Nectar is a sugar-rich liquid produced by plants in glands called nectaries or nectarines, either within the flowers with which it attracts pollinating animals, or by extrafloral nectaries, which provide a nutrient source to animal mutualis ...

. In exchange for food and shelter, ants aid the myrmecophyte in

pollination Pollination is the transfer of pollen from an Stamen, anther of a plant to the stigma (botany), stigma of a plant, later enabling fertilisation and the production of seeds, most often by an animal or by Anemophily, wind. Pollinating agents can ...

seed dispersal In Spermatophyte plants, seed dispersal is the movement, spread or transport of seeds away from the parent plant. Plants have limited mobility and rely upon a variety of dispersal vectors to transport their seeds, including both abiotic vector ...

, gathering of essential

nutrients A nutrient is a substance used by an organism to survive, grow, and reproduce. The requirement for dietary nutrient intake applies to animals, plants, fungi, and protists. Nutrients can be incorporated into cells for metabolic purposes or excr ...

, and/or defense. Specifically, domatia adapted 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 mutualism

In obligate mutualisms, both of 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 Oceans, t ...

''. All species of this genus provide food for ants in various forms, but only the obligate species produce domatia. Some of the most common species of myrmecophytic ''Macaranga'' interact with ants in the genus '' Crematogaster''. ''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 mutualism

Facultative mutualism is a type of relationship where the survival of both parties (plant and ants, in this instance) is not dependent upon the interaction. Both organisms can survive without the other species. Facultative mutualisms most often occur in plants that have

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 ...

has not occurred. For example,

Old World The "Old World" is a term for Afro-Eurasia that originated in Europe , after Europeans became aware of the existence of the Americas. It is used to contrast the continents of Africa, Europe, and Asia, which were previously thought of by thei ...

legumes A legume () is a plant in the family Fabaceae (or Leguminosae), or the fruit or seed of such a plant. When used as a dry grain, the seed is also called a pulse. Legumes are grown agriculturally, primarily for human consumption, for livestock for ...

that were introduced to

North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and th ...

can be protected by ants that originated from a different region.

Structural adaptations of myrmecophytes

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 A leaf ( : leaves) is any of the principal appendages of a vascular plant stem, usually borne laterally aboveground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", while the leaves, st ...

, and spines of plants. Many different genera of plants offer domatia. Plants of the genus ''

Acacia ''Acacia'', commonly known as the wattles or acacias, is a large genus of shrubs and trees in the subfamily Mimosoideae of the pea family Fabaceae. Initially, it comprised a group of plant species native to Africa and Australasia. The genus nam ...

'' 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 A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpart ...

and encroaching

vine A vine (Latin ''vīnea'' "grapevine", "vineyard", from ''vīnum'' "wine") is any plant with a growth habit of trailing or scandent (that is, climbing) stems, lianas or runners. The word ''vine'' can also refer to such stems or runners themsel ...

s. Domatia can also be found within the

tubers Tubers are a type of enlarged structure used as storage organs for nutrients in some plants. They are used for the plant's perennation (survival of the winter or dry months), to provide energy and nutrients for regrowth during the next growing s ...

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 ...

s of a seedling swells to form a hollow, chambered structure that can become inhabited by ants. The plant family

Rubiaceae The Rubiaceae are a 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 interpetiolar stipules a ...

contains the most commonly known tuberous myrmecophyte, '' Myrmecodia''. A-cornigera

Food bodies

Some plants produce food bodies for use by other organisms. These small epidermal structures contain a variety of nutrients that are removed and consumed by foragers. Food bodies are identified by the main

nutrient A nutrient is a substance used by an organism to survive, grow, and reproduce. The requirement for dietary nutrient intake applies to animals, plants, fungi, and protists. Nutrients can be incorporated into cells for metabolic purposes or excre ...

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 ''

'' plants and have relatively high

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, res ...

content. Beccarian bodies are found on young leaves of the genus ''

'' and are especially rich in

lipids Lipids are a broad group of naturally-occurring molecules which includes fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, phospholipids, and others. The functions of lipids in ...

. Lipids are also the main nutrient found in

pearl bodies A pearl is a hard, glistening object produced within the soft tissue (specifically the mantle) of a living shelled mollusk or another animal, such as fossil conulariids. Just like the shell of a mollusk, a pearl is composed of calcium car ...

, 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 the last type of food body, 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. The polysaccharide structure represents the main storage form of glucose in the body. Glycogen functions as one of ...

. Glycogen is the principal storage

carbohydrate In organic chemistry, a carbohydrate () is a biomolecule consisting of carbon (C), hydrogen (H) and oxygen (O) atoms, usually with a hydrogen–oxygen atom ratio of 2:1 (as in water) and thus with the empirical formula (where ''m'' may o ...

found in

animal Animals are multicellular, eukaryotic organisms in the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually, and go through an ontogenetic stage ...

s and is extremely rare in plants. Cherry petiole glands

Extrafloral nectaries

Extrafloral nectaries Nectar is a sugar-rich liquid produced by plants in glands called nectaries or nectarines, either within the flowers with which it attracts pollinating animals, or by extrafloral nectaries, which provide a nutrient source to animal mutualis ...

are sugar-producing glands found outside the

flower A flower, sometimes known as a bloom or blossom, is the reproductive structure found in flowering plants (plants of the division Angiospermae). The biological function of a flower is to facilitate reproduction, usually by providing a mechanis ...

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

, stems, and

twig A twig is a thin, often short, branch of a tree or bush. The buds on the twig are an important diagnostic characteristic, as are the abscission scars where the leaves have fallen away. The color, texture, and patterning of the twig bark ar ...

s. These secreting structures are often non-exclusive in that

nectar Nectar is a sugar-rich liquid produced by plants in glands called nectaries or nectarines, either within the flowers with which it attracts pollinating animals, or by extrafloral nectaries, which provide a nutrient source to animal mutualist ...

can be taken by a variety of animals; however, in some obligate myrmecophyte plants such as '' Acacia collinsii'', 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'', shows a decreased loss of leaf tissue on branches protected by ants, and an increase in number of seeds produced.

Types of ant-plant interactions

Ants as pollinators

Unlike their

bee Bees are winged insects closely related to wasps and ants, known for their roles in pollination and, in the case of the best-known bee species, the western honey bee, for producing honey. Bees are a monophyletic lineage within the superfami ...

relatives, ants rarely

pollinate Pollination is the transfer of pollen from an anther of a plant to the stigma of a plant, later enabling fertilisation and the production of seeds, most often by an animal or by wind. Pollinating agents can be animals such as insects, birds, a ...

plants. Various assumptions 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 Pollination is the transfer of pollen from an anther of a plant to the stigma of a plant, later enabling fertilisation and the production of seeds, most often by an animal or by wind. Pollinating agents can be animals such as insects, bird ...

, b) ants do not systematically forage like 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'' can only be pollinated by its winged male ant partner ('' Myrmecia urens''). Afzelia africana1

Ants and seed dispersal

Myrmecochory Myrmecochory ( (sometimes myrmechory); from grc, μύρμηξ, mýrmēks ("ant") and ''khoreíā'' ("circular dance") is seed dispersal by ants, an ecologically significant ant–plant interaction with worldwide distribution. Most myrmec ...

, literally translated as "ant-dispersal," is the collection and dispersal of

seeds A seed is an embryonic plant enclosed in a protective outer covering, along with a food reserve. The formation of the seed is a part of the process of reproduction in seed plants, the spermatophytes, including the gymnosperm and angiosperm ...

by ants. Ants disperse more than 30% of the spring-flowering

herbaceous plants Herbaceous plants are vascular plants that have no persistent woody stems above ground. This broad category of plants includes many perennials, and nearly all annuals and biennials. Definitions of "herb" and "herbaceous" The fourth edition of ...

in eastern

. Both the plant and the ant benefit in this scenario. The ants are provided with an elaiosome, a detachable food body found on the surface of the seed. Elaiosomes have diverse compositions, usually high in

and

fatty acids In chemistry, particularly in biochemistry, a fatty acid is a carboxylic acid with an aliphatic chain, which is either saturated and unsaturated compounds#Organic chemistry, saturated or unsaturated. Most naturally occurring fatty acids have an B ...

, but also containing

amino acids Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha am ...

sugars Sugar is the generic name for sweet-tasting, soluble carbohydrates, many of which are used in food. Simple sugars, also called monosaccharides, include glucose, fructose, and galactose. Compound sugars, also called disaccharides or double ...

, and

. The ants remove the elaiosome once the seed has been transported to the

colony In modern parlance, a colony is a territory subject to a form of foreign rule. Though dominated by the foreign colonizers, colonies remain separate from the administration of the original country of the colonizers, the '' metropolitan state' ...

. As a result, the seeds are safely placed in nutrient-rich substrate protected from

predator Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill t ...

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

from debris piles left by ant nests or, in the case of '' Nepenthes bicalcarata'', from ant egesta. The tropical tree ''

peltata'' obtains 98% of its nitrogen from the waste deposited by its ant counterparts. A recent study by Chanam et al.Chanam, J., Sheshshayee, M.S., Kasinathan, S., Jagdeesh, A., Joshi, K.A., Borges, R.M., "Nutritional benefits from domatia inhabitants in an ant–plant interaction: interlopers do pay the rent" (Functional Ecology, 2014), showed that plants bearing domatia can be favoured even before the establishment of a specialised protection-based symbiosis, as nutritional benefits can be provided by a motley set of domatia residents that could include multiple species of ant (including protective, non-protective and even plant-damaging species such as ''Crematogaster dohrni'') as well as other invertebrates, including as arboreal

earthworm An earthworm is a terrestrial invertebrate that belongs to the phylum Annelida. They exhibit a tube-within-a-tube body plan; they are externally segmented with corresponding internal segmentation; and they usually have setae on all segments. T ...

s. Only some individuals of the myrmecophyte '' Humboldtia brunonis'' (found in the Western Ghats of

India India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area, the List of countries and dependencies by population, second-most populous ...

) bear domatia on some of their branches, while all individuals produce extrafloral nectar. Each domatium is formed by modified swollen and hollow internodes. These domatia have a self-opening slit that allows access to the domatium interior and are prone to interloping residents (including many species of non-protective ants and the arboreal earthworm ''Perionyx pullus'') in addition to the protective ants. Earlier studies established that domatia-bearing ''H. brunonis'' plants have greater fruit set, hence greater reproductive success, than ''H. brunonis'' plants without domatia. Plant tissues near domatia received 17% and 9% of their nitrogen from the ants (protective and non-protective) and the earthworm respectively. The absorbed nutrients also travelled to distant branches; hence, fruit set was not different between branches with and without domatia. This study demonstrated that non-protective interlopers in the domatia still contribute to the greater wellbeing of the plant by contributing to plant nutrition. WeaverAntsAgainstRedAnt

Ants as defense

Since plants provide essential

resources Resource refers to all the materials available in our environment which are technologically accessible, economically feasible and culturally sustainable and help us to satisfy our needs and wants. Resources can broadly be classified upon their av ...

for ants, the need to protect the plant and those resources is extremely important. Many myrmecophytes are defended from both

and other competing plants by their ant symbionts. ''

Acacia cornigera ''Vachellia cornigera'', commonly known as bullhorn acacia (family Fabaceae), is a swollen-thorn tree native to Mexico and Central America. The common name of "bullhorn" refers to the enlarged, hollowed-out, swollen thorns (technically called sti ...

'', for example, is thoroughly guarded by its obligate ant partner, '' Pseudomyrmex ferruginea''. 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 Pruning is a horticultural, arboricultural, and silvicultural practice involving the selective removal of certain parts of a plant, such as branches, buds, or roots. The practice entails the ''targeted'' removal of diseased, damaged, dead, ...

any trespassers. The ants keep the plant free from other insects and vertebrate herbivores, from invading fungi and also from other plants.