Most edible mushrooms are relatively small, but in West Africa as well as Zambia, there’s one particularly enormous species that outgrows all the rest of them.

Termitomyces titanicus. A rather fitting name for such a huge species.

In Zambia, where mushroom-gathering is an important part of life, the Termitomyces titanicus is especially held in high regard. While the largest fungus (and organism) in the world is of the genus Armillaria and is currently consuming Oregon on 1,000 hectares, Termitomyces titanicus is the world’s largest edible mushroom, with a cap that can measure a little more than three feet (one meter) across.

Interestingly, this giant mushroom species was unknown to Western science prior to 1980, despite its size and the fact it was a common item in native markets.

This family living in Zambia purchased this giant specimen on the road to Lusaka, the capital city.

The name Termitomyces refers to how the mushroom grows inside a termite hill. The mushrooms in this genus have a symbiotic relationship with termites and grow on their fecal matter, breaking down plant material as food for them. Decayed mushroom tissue is another food source for the termites.

In turn, the fungi associated with termites receive a steady supply of plant material, in a location with fine-tuned temperature and moisture content optimal for growth.

The mushrooms are connected to the heart of a colony of fungal breeding termites. Image credit: Aanen and de Beer

But why does the mushroom grow so big? Well for one, it acquires a huge amount of resources from its insect mutualist, as termite colonies can reach densities in the millions, with countless individuals foraging for organic material to feed them. But it’s size is not only due the large amounts of energy it obtains: this horizontally transferred fungus must spread enough spores to be found by suitable termite species. In low producing savanna ecosystems, the distribution of termite mound may be quite patchy. So, to ensure that it gets a good chance at finding a suitable substrate, the fungus has evolved one of, if not the, largest mushrooms on the planet. The larger the mushroom, the more spores it produces, making it easier for initial termite foragers to actually find them.