A seemingly unremarkable fern from New Caledonia, Tmesipteris oblanceolata, has been awarded the Guinness World Record for having the largest genome of any known organism. This modest fern, which only grows on this remote Pacific island, contains more than 50 times the DNA of humans.
Staggering Genomic Proportions
The DNA in each cell of Tmesipteris oblanceolata, if unraveled, would extend to 106 meters (350 feet)—taller than the tower housing London’s Big Ben bell. The fern’s genome measures an astonishing 160 gigabase pairs (Gbp), which is seven percent larger than the previous record holder, the Japanese flowering plant Paris japonica, and significantly surpasses the human genome’s 3.1 Gbp. In comparison, human DNA, if unraveled, would stretch about two meters long.
Researchers, including study co-author Ilia Leitch from the UK’s Royal Botanic Gardens Kew, were astonished by the discovery. “We thought we’d already reached the biological limit. We’re really pushing at the extremes of biology,” Leitch remarked. The fern, which grows to a modest height of five to ten centimeters, was studied on New Caledonia’s main island, Grand Terre, with local scientists’ assistance. The findings were published in the journal iScience.
The fern’s record-setting genome has been officially recognized by Guinness World Records. Adam Millward, managing editor of Guinness World Records, noted that this “innocuous-looking” fern demonstrates that record holders are not always the most visually striking.
Understanding the Genome
A genome comprises all of an organism’s DNA, which acts as a set of instructions for living and surviving. Despite having cataloged the genome sizes of around 20,000 organisms, scientists still know relatively little about many of them. Among animals, the marbled lungfish has the largest genome at 130 Gbp, while the carnivorous plant Genlisea aurea has one of the smallest at just 0.06 Gbp.
Having a large genome is not necessarily advantageous. Larger genomes require larger cells to contain the DNA, which can slow down growth and complicate reproduction. This is why plants with massive genomes are often slow-growing and less adaptable to environmental changes. Genome size can affect a plant’s response to climate change, land use changes, and other challenges.
Mystery of DNA Function
The function of much of the DNA in large genomes like that of Tmesipteris oblanceolata remains unclear. Some scientists refer to this excess DNA as “junk DNA,” though this term might reflect our current ignorance rather than the DNA’s lack of function. Leitch and her team are puzzled by how organisms with such extensive DNA manage to function, while Jonathan Wendel, a botanist at Iowa State University, emphasized that understanding genome size variation and its evolutionary implications is an ongoing scientific challenge.
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