Mistletoe – the plant that encourages kissing at Christmas – is actually a parasite and has an unusual feeding strategy, new research suggests.

Like other plants, mistletoe can use sunlight to create its own food, a process called photosynthesis.

But it prefers to siphon water and nutrients from other trees and shrubs, using false roots to invade its hosts, according to a new study.

They seem to know when they're attacking the same host, and can reduce the virulence of their attack

University of California Riverside plant-insect ecologist Paul Nabity said: “Plants are autotrophic, they make their own food. Humans are heterotrophic, we eat it.

“Mistletoe are mostly heterotrophic, but they can switch if they want to.”

He added: “They seem to know when they’re attacking the same host, and can reduce the virulence of their attack.”

The Christmas mistletoe is a European species that tends to attack apple and other hardwood trees in central California.

Researchers examined a native species of mistletoe found throughout the Sonoran and Mojave deserts that often grows on acacia, palo verde or mesquite trees.

When researchers removed one of two mistletoes from a branch, they found the plant left behind did not increase its photosynthesis.

In some cases it reduced its water intake, according to the paper published in Current Biology.

Dr Nabity explained: “It appears that the remaining mistletoe recognised it was no longer competing for resources.”

Birds are known to feed from and guard a fruiting mistletoe and in the process, excrete seeds into the same tree from which they came.

A tree full of related mistletoes increases the parasite load for the host, but the infection may not be as severe as it otherwise would be if infected with unrelated plants.

Researchers say communication among mistletoes is possible through a variety of methods.

They are connected to a host’s xylem – the tissue that trees use to move water and nutrients from the roots.

It is possible the mistletoes send messages using the xylem, and it is also possible they may smell one another, Dr Nabity says.

Plants produce chemical compounds and release them through their pores.

These compounds evaporate quickly into the air, sending signals that can be received down wind.

But Dr Nabity said that however mistletoe communicates, it doesn’t necessarily need to be removed from infected trees.

“Don’t remove mistletoe because you think they’re all bad,” he said