Ten organisms have a genome surpassing 100 billion bp, that is 33 times larger than ours. Of these genomic giants, the three largest are plants. Small, unassuming plants that you could grow in your garden.

Let’s take a look:

3rd place: the long fork fern (Tmesipteris obliqua), with a genome of over 147.3 billion bp [3] or 46 human genomes. This plant’s genome unwinds over 97 meters, 319 feet, which is slightly taller than the Big Ben! This fern inhabits humid, shady environments in Australia, where its fronds grow up to 65 cm, 2 feet.

The long fork fern

2nd place: the Japanese canopy plant (Paris japonica), with a genome of 148.9 billion bp [4] or 47 human genomes. Its DNA stretches over 99 meters, 325 feet, which is taller than Michael Jordan on top of Big Ben! This one is a flowering plant growing in Japan’s mountains, where it reaches 80 cm, less than 3 feet.

The Japanese canopy plant

1st place: as of May 2024, the title of giant among genomic giants belongs to another fern, the hanging fork fern (Tmesipteris oblanceolata subspecies linearifolia). Its DNA boasts 160.5 billion bp [5], or 50 human genomes. Such a giant spans 107 meters, 350 feet. That’s taller than a light pole on top of Big Ben! The tiny hanging fork fern lives in New Caledonia and neighbouring islands.

The hanging fork fern

Is 160 billion bp the absolute ceiling or could another giant dethrone the hanging fork fern?

Well, we don’t know, but practical costs of a giant genome outweigh theoretical advantages.

Genomes balloon to giant sizes due to the accumulation of non-coding repetitive DNA and, in plants, to whole-genome duplications. While extra DNA repeats offer no benefit, an extra copy of the genome (polyploidy) might make a species more adaptable to changes—evolution can repurpose duplicated genes to new functions without losing current ones. However, evolutionary flexibility comes at immense costs of nutrients to build the genome and of energy to sustain DNA replication, transcription and repair [6]. As a result, genomic giants grow more slowly and are more sluggish than organisms with smaller genomes.

Yes, a genome can be too large, but living beings are full of surprises. Scientists remain on the hunt for a giant that pushes forward genomic boundaries and our understanding of biology.

PS: here is the list of the other seven organisms with a genome surpassing 100 billion bp (adapted from [6]).