Record-breaking tiny fern has largest genome of any organism on Earth

WATCH: Study co-author Ilia Leitch talks to CGTN about this incredible plant

A tiny fern plant that contains the largest amount of DNA stored in the nucleus of any living organism on the planet has been discovered.

Found in New Caledonia on a remote Pacific island, the tiny fork fern now holds three Guinness World Record titles.

If its DNA was unraveled it would reach just over 100 meters – higher than the tower that's home to the world-famous Big Ben bell in London. For comparison, if a human being's DNA was unraveled; it would only be around 2 meters tall, the height of an average door.

The New Caledonian fern - its full name is Tmesipteris oblanceolata - has over 50 times more DNA packed into the nucleus of its cells than humans do.

The fern's genome weighed in at a whopping 160 gigabase pairs (Gbp), the measurement for DNA length. That is seven percent larger than the previous record holder, the Japanese flowering plant Paris japonica.

The human genome is a relatively puny 3.1 Gbp.

Study co-author Ilia Leitch, a researcher at the UK's Royal Botanic Gardens Kew, said the team was "really surprised to find something even bigger than Paris japonica."

She told CGTN Europe: "This fern has pushed the limit - we are right at the extremes of what biology can do.

"In environments that are changing, such as with climate change or bio diversity loss, they are less adaptable and more constrained. I do believe this species is going to be pushing on the edge of being unlikely to survive huge changes in the environment."

The fern, which grows five to 10 centimetres tall, is only found in New Caledonia, a French Pacific territory which has recently seen unrest.

Two members of the research team traveled to the main island, Grand Terre, in 2023 and worked with local scientists for the study, which was published in the journal iScience.

What's a genome?

Humans are estimated to have more than 30 trillion cells in our bodies. Within each of those cells is a nucleus which contains DNA, which is like a "book of instructions that tells an organism like ourselves how to live and survive", Leitch said.

All of an organism's DNA is called its genome. So far, scientists have estimated the genome size of around 20,000 organisms, just a fraction of life on Earth.

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Among animals, the marbled lungfish has the largest, with 130 Gbp. While plants have the biggest genomes, they can also have incredibly small ones. The carnivorous Genlisea aurea's genome is just 0.06 Gbp.

For plants, bigger cells mean things like the pores of leaves have to be larger, which can make them grow more slowly. It is also trickier to make new copies of all that DNA, limiting their reproductive abilities.

This means the biggest genomes are seen in slow-growing, perennial plants which cannot easily adapt to adversity or contend with competition.

Genome size can therefore affect how plants respond to climate change, changing land use and other environmental challenges caused by humans, Leitch added.

Super DNA

Jonathan Wendel, a botanist at Iowa State University not involved in the research, agreed it was "astonishing" how much DNA the fern is packing.

But this only "represents the first step", he said.

"A great mystery is the meaning of all of this variation - how do genomes grow and shrink, and what are the evolutionary causes and consequences of these phenomena?"

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