The fig has a reproductive system unlike most other flowering species. Instead of a typical open bloom, the fig is an inverted flower cluster, known scientifically as a syconium. The flowers are hidden on the inside of what most people consider the fruit. Because the flowers are enclosed, the fig cannot rely on typical pollinators like bees or butterflies for fertilization. This arrangement necessitates a specialized mechanism for reproduction that relies entirely on a single, tiny partner.
Understanding the Fig’s Unique Anatomy
The fig structure, or syconium, is a hollow, fleshy receptacle that develops from a modified stem. Its interior wall is lined with hundreds of minute, individual flowers, making the fig an inflorescence, not a true fruit in the botanical sense. These flowers are sessile, meaning they are attached directly to the inner surface without a stalk.
The syconium is almost completely sealed off, forming a protective chamber for the developing flowers and seeds. The only natural entry point is a small, scale-lined opening at the apex called the ostiole. This opening is guarded by overlapping bracts, creating a tight passage that regulates what can enter the inner cavity.
This anatomical design provides the plant with significant protection for its reproductive parts against general herbivores and pests. However, it also creates the problem of pollination, as external agents cannot access the hidden flowers. The plant’s design functions as a secure nursery.
The Obligate Partnership Between Fig and Wasp
The reproductive cycle of the fig tree (Ficus) is interwoven with a specific group of insects, the fig wasps (family Agaonidae). This biological relationship is an obligate mutualism: neither species can complete its life cycle without the other. The fig depends on the wasp for pollination, and the wasp depends on the fig for a protected site to lay its eggs.
This specialized dependency is the result of millions of years of co-evolution, with evidence suggesting the partnership originated between 70 and 90 million years ago. Each of the over 750 Ficus species relies on its own unique species of pollinating wasp. The fig has evolved to offer a nursery for the wasp larvae.
The fig uses volatile organic compounds to indicate when a syconium is receptive to pollination. This species-specific scent acts as an attractant, guiding the female wasp to the correct host tree.
The Specific Stages of Pollination and Fertilization
The process begins when a female fig wasp, carrying pollen from her birthplace fig, locates a receptive syconium. She gains entry by squeezing through the narrow ostiole, a difficult feat that often results in her wings and antennae being torn off. Once inside the dark chamber, she can no longer leave.
The female wasp crawls across the inner wall, performing two distinct tasks. She deposits the pollen she carried onto the stigmas of the female flowers, fertilizing the fig’s seeds. Her primary goal is to lay her eggs by inserting her ovipositor into the ovaries of some flowers.
Fig flowers display varying style lengths. The wasp can only successfully lay an egg in the short-styled female flowers, as their styles are shorter than her ovipositor. These flowers are transformed into galls, which provide food and shelter for the developing wasp larvae.
Conversely, the long-styled female flowers have styles too long for the wasp’s ovipositor to reach the ovary. These flowers are pollinated by the transferred pollen but are spared from egg-laying, allowing them to develop into viable seeds.
Once the eggs are laid, the mother wasp dies inside the syconium. The eggs hatch into larvae, which develop inside the protective galls. The wingless male wasps emerge first, seeking out and mating with the females while they are often still inside their galls.
The male wasps use their mandibles to chew exit tunnels through the wall of the syconium to the outside. The males then die, having never left the fig’s interior. The newly fertilized female wasps emerge from their galls, collecting pollen from the now-mature male flowers lining the syconium near the exit tunnels. The females then fly out through the tunnels, carrying the pollen to begin the cycle in a different fig.
Not All Figs Require Wasp Fertilization
The common edible fig, Ficus carica, does not always require the wasp-mediated process to produce fruit suitable for human consumption. Many commercially grown varieties, such as ‘Brown Turkey’ or ‘Black Mission,’ are cultivated to be parthenocarpic. This means the fruit develops and ripens without the need for fertilization or seed development.
These parthenocarpic figs, which are typically seedless, will mature and become sweet even if no wasp has entered. This trait allows fig cultivation in regions where the specific pollinating wasp, Blastophaga psenes, does not naturally exist. Smyrna-type figs, however, are non-parthenocarpic and still require the wasp for fruit development.
The wild fig varieties, or caprifigs, serve as the host and nursery for the wasp’s life cycle. In these figs, the dead mother wasp is not an inedible insect remnant. The fig produces a powerful protein-digesting enzyme called ficain, which breaks down the wasp’s body. The dissolved wasp is entirely absorbed by the ripening fig, converting the insect’s organic matter into nutrients.