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Plant 211


Ficus benghalensis (Moraceae)

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Banyan



The banyan is a fig tree that is native to India and is considered sacred in the subcontinent. It has the distinction of being one of the world's largest trees by canopy area. Furthermore, some of these trees are known to be thousands of years old. One of the biggest banyans, in Andhra Pradesh, would cover the entire area of the Oxford Botanic Garden. The banyan achieves this feat by aerial roots which grow down from the branches to the ground. In Paradise Lost (1667), John Milton describes the phenomenon thus:

'Branching so broad and long, that in the ground [/] The bended twigs take root, and daughters grow [/] About the mother tree, a pillared shade [/] High over-arched, and echoing walks between'.

The tree's common name is derived from the merchants who traditionally traded under its canopy.

Hundreds or thousands of tiny fig flowers are enclosed within a bulbous structure that has one tiny hole (ostiole) at its apex. When mature, this structure forms a unique type of multiple fruit called a synconium. The pollination of fig flowers requires specialised pollinators called fig wasps; usually one wasp species pollinates one fig species. Banyans are pollinated by the agaonid wasp Eupristina masoni.

A fertilised female wasp squeezes through the ostiole, often losing her wings and antennae in the process. Inside, she lays her eggs in some of the flowers, disperses the pollen covering her body and then dies; her remains are digested by the fig. The pollen will fertilise the female flowers, producing tiny single-seeded fruits. Eventually the wasp eggs hatch, the males and females mate and then take on different roles. The winged females collect pollen, whilst the wingless males make a hole in the fig, so the female can escape, and then die; males spend their entire lives in a single fig. Ripe figs are collections of thousands of tiny fruits. Figs are dispersed by frugivores such as birds and mammals and are major sources of food for these animals in tropical forests. In the case of banyans, mature figs are particularly important in the diets of the Indian myna bird.

Banyans are widely cultivated in the tropics as novelties and for shade. However, where the pollinator occurs, banyans can become invasive. For example, they have become serious weeds in parts of Florida, USA, after plants were first discovered in the mid 1980s and the pollinating wasp was accidentally introduced.

Further reading

Midya S and Brahmachary RL 1991. The effect of birds upon germination of banyan (Ficus bengalensis() seeds. Journal of Tropical Ecology 7: 537-538.

Jander K and Herre E 2010. Host sanctions and pollinator cheating in the fig tree-fig wasp mutualism. Proceedings of the Royal Society B: Biological Sciences 277: 1481-1488.

PIER 2000. Invasive plant species: Ficus benghalensis L., Moraceae. Pacific Island Ecosystems at Risk.


Stephen Harris