Researchers studying the fork fern Tmesipteris oblanceolata have confirmed it holds the largest known genome of any living organism — more than 50 times the size of the human genome — a finding that is reshaping how botanists understand pteridophyte evolution and the limits of genetic complexity. The discovery, formally announced in 2024 and continuing to drive new research through this year, was led by a team from the Royal Botanic Gardens, Kew and the Institut Botànic de Barcelona, who measured the species’ DNA content at a staggering 160.45 gigabase pairs.
A Tiny Plant With a Colossal Genetic Library
At first glance, Tmesipteris oblanceolata is unremarkable. The slow-growing epiphytic fern, native to the forests of New Caledonia, rarely exceeds 10 centimetres in length and clings unobtrusively to the trunks of larger trees. Yet within each of its cells lies a genome so vast that, if unspooled, the DNA would stretch nearly 100 metres — taller than Big Ben. The finding, announced by the Royal Botanic Gardens, Kew, dethrones the previous record-holder, the Japanese flowering plant Paris japonica, and earned the species a place in the Guinness World Records.
For pteridologists — botanists who specialise in ferns and their allies — the discovery is more than a curiosity. It raises pressing questions about why some plants accumulate enormous quantities of genetic material while others streamline their genomes. The genus Tmesipteris, considered one of the most ancient lineages of vascular plants, has now become a focal point for research into genome gigantism.
Why Genome Size Matters
Contrary to intuition, larger genomes do not necessarily mean more genes or greater biological complexity. Much of the additional DNA in species like Tmesipteris oblanceolata consists of non-coding sequences and repetitive elements. However, carrying such a heavy genetic load comes with costs. Studies have shown that plants with oversized genomes tend to grow more slowly, occupy narrower ecological niches, and may be more vulnerable to environmental stress and extinction.
Dr Ilia Leitch, senior research leader at Kew and a co-author on the study, has emphasised that understanding genome size variation is critical for conservation biology. As reported by the BBC, Leitch noted that “the bigger the genome, the more time it takes to replicate,” meaning species with massive genomes may struggle to adapt to rapidly changing climates. With New Caledonia’s forests facing pressure from mining and habitat loss, the survival of Tmesipteris populations is far from guaranteed.
Implications for Pteridology and Evolutionary Biology
The fork ferns belong to the Psilotaceae, a family with deep evolutionary roots stretching back hundreds of millions of years. Their reduced morphology — they lack true roots and have only simple leaf-like structures — once led botanists to consider them living fossils, akin to the earliest land plants. Modern molecular phylogenetics has since placed them firmly within the eusporangiate ferns, but their unusual biology continues to intrigue researchers.
The new genomic data, published in the journal iScience, will allow scientists to investigate the mechanisms — including polyploidy and the proliferation of transposable elements — that have driven such extraordinary genome expansion. It also opens questions about whether even larger genomes remain undiscovered in remote tropical floras.
What Comes Next
Botanists are now calling for expanded surveys of underexplored fern lineages, particularly in biodiversity hotspots like New Caledonia, Madagascar, and parts of Southeast Asia. Sequencing such enormous genomes presents formidable technical challenges, but advances in long-read sequencing technology are bringing once-impossible projects within reach. Conservationists, meanwhile, are urging stronger protections for the obscure species that hold these genetic record-breakers, arguing that losing them would mean losing irreplaceable chapters of evolutionary history.
The story of Tmesipteris oblanceolata is a reminder that some of biology’s most extraordinary phenomena are hidden in the smallest, most easily overlooked corners of the natural world — and that pteridology, often considered a niche discipline, continues to deliver discoveries with global scientific significance.
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