LONDON, Nov. 28 (Xinhua) -- Scientists have found a new type of ant-plant symbiosis in Fiji, with one species of ants farming a plant called Squamellaria.

The Philidris nagasau ants not only live in and eat the plant, they also actively and exclusively plants the seeds and fertilizes the seedlings of six species of Squamellaria, scientists said in an article published in the British journal Nature on Nov. 21.

Squamellaria is a brown and bulbous plant that lives on and sticks out from tree branches.

As ants eat the fruit of and take shelter in the plant, they also fertilize Squamellaria with their excrement, harvest and plant its seeds, guard the growth of seedlings, live in the mature plants and repeat the cycle.

Guillaume Chomicki, a botanist at the Ludwig-Maximilians University in Munich, Germany, who is also the lead author of the study, told Nature that the ants don't hang out in other plants, suggesting that the ants and plants are dependent on each other.

Cultivation by certain kinds of animals is quite common in nature, as the relations can be seen in leaf-cutter ant farming fungus or Acropyga ant shepherding mealybugs. But the symbiosis between Philidris nagasau ants and Squamellaria is unique as they cannot live without each other.

"We already have ants that disperse seeds, and have ants that feed plants, but we've never had a case where they farm a plant they can't live without," the journal quoted Brian Fisher, an entomologist-in-residence at the California Academy of Sciences of the United States, as saying.

After reconstructing the evolutionary history, scientists assumed that careful cultivation by ants has changed the structure of Squamellaria, just like humans changing the structures of agricultural products such as beans and corn.