Tiny fern breaks record for largest genome on Earth

The fern species Tmesipteris oblanceolata from New Caledonia was found to have more than 50 times more DNA in each cell than humans. According to new research, its genome size is 160.45 gigabase pairs. Credit: Pol Fernandez.

In a groundbreaking discovery, researchers have identified a tiny fern with the largest genome of any living organism.

This species, known as Tmesipteris oblanceolata, has been found to contain more than 100 meters of unraveled DNA in each cell, which is over 50 times more DNA than humans.

The findings were published in the journal iScience by scientists from the Royal Botanic Gardens, Kew, and the Institut Botànic de Barcelona (IBB-CSIC) in Spain.

  1. oblanceolata, a rare fern species found in New Caledonia, an island in the Southwest Pacific, has dethroned the previous record-holder, the Japanese flowering plant Paris japonica, which held the record since 2010.

This fern now holds three Guinness World Records titles for the Largest Plant Genome, Largest Genome, and Largest Fern Genome.

The genus Tmesipteris includes about 15 species, primarily found across Pacific Islands and Oceania.

Until now, scientists had only estimated the genome sizes of two other Tmesipteris species, T. tannensis and T. obliqua, which have very large genomes of 73.19 and 147.29 gigabase pairs (Gbp) respectively.

In 2023, Dr. Jaume Pellicer and Dr. Oriane Hidalgo, the lead researchers, traveled to New Caledonia to collect samples of Tmesipteris.

They isolated the nuclei of thousands of cells, stained them with a dye, and measured the DNA.

The more dye that bound to the DNA, the larger the genome. Their analysis revealed that T. oblanceolata has a genome size of 160.45 Gbp, which is about 7% larger than P. japonica’s genome of 148.89 Gbp.

When unraveled, the DNA from each cell of T. oblanceolata would stand taller than the Elizabeth Tower in London, which houses Big Ben and is 96 meters tall. For comparison, the human genome contains about 3.1 Gbp across 23 chromosomes, and when stretched out, each cell’s DNA measures about 2 meters.

Dr. Pellicer explains, “Tmesipteris is a unique and fascinating small genus of ferns, whose ancestors evolved about 350 million years ago—well before dinosaurs.

This fern grows mainly on the trunks and branches of trees and is found in specific regions like Oceania and several Pacific Islands. Breaking the size record of Paris japonica was a long shot, but this discovery has exceeded our expectations.”

To date, scientists have estimated the genome sizes of more than 20,000 eukaryotic organisms, revealing a wide range of genome sizes.

These variations in genome size impact not only the anatomy of organisms but also how they function, evolve, and adapt to their environments.

In animals, some of the largest genomes are found in the marbled lungfish (Protopterus aethiopicus) at 129.90 Gbp and the Neuse River waterdog (Necturus lewisi) at 117.47 Gbp. Six of the largest-known eukaryotic genomes are held by plants, including the European mistletoe (Viscum album) at 100.84 Gbp.

Having a larger genome is usually not advantageous. Plants with large amounts of DNA tend to be slow-growing perennials, less efficient at photosynthesis, and require more nutrients to grow. These factors may influence their ability to adapt to climate change and increase their risk of extinction.

Dr. Ilia Leitch, Senior Research Leader at RBG Kew, says, “It’s incredible that this tiny, unassuming fern has such a massive genome. This discovery highlights the diversity of plants at the DNA level and their intrinsic value in global biodiversity.

It also raises exciting questions about the biological limits, which we hope to explore further.”

Adam Millward, Managing Editor of Guinness World Records, adds, “To think this small fern has 50 times more DNA than humans is a humbling reminder of how much we still have to learn about the plant kingdom.”