Experts say a special breed found in Madagascar could hold the key to keeping them alive.
But there are only five known trees in existence.
Scientists are racing to develop new banana varieties strong enough to survive Panama disease, which is a major threat to banana crops around the world.
Because bananas are clones, the disease is able to spread very quickly from one to another.
It is currently wreaking havoc with crops in Asia – but could wipe out the world’s supply if it spreads to America.
Richard Allen, senior conservation assessor at the Royal Botanic Gardens, Kew, told the BBC: "It doesn't have Panama disease in it, so perhaps it has genetic traits against the disease.
"We don't know until we actually do research on the banana itself, but we can't do the research until it's saved."
The Madagascan variety isn’t suitable for eating – but researchers hope to create a new type of banana through cross-breeding.
But the few remaining trees are stranded on the edge of Madagascan forests, threatened by logging, fires and farming.
