A genome is an organism's hereditary information—its DNA—and Biologists have been studying them since the early 20th century. Genome sizes vary a lot, and the numbers can be very surprising. To wit, the record for largest genome goes to ... a plant! A rare flowering plant called Paris japonica has a genome 50 time longer than that of humans, and the longest known genome of any organism.
Scientists have measured the genome of Paris japonica, a slow-growing canopy plant, to contain about 150 billion base pairs, and weigh 152.23 picograms (trillionth of a gram). The plant's genome, if extracted and extended, would be "taller than Big Ben," estimates a research scientist at Royal Botanic Gardens, Kew. By contrast, human DNA would measure about two meters.
As far as the plant is concerned, the superlative title is not without consequences. Longer genomes take longer to reproduce, which can correlate to the vulnerability of a species. Paris japonica is already rare. According to the Global Biodiversity Information Facility, it has been identified in seven locations, all in sub-alpine Japan. “In plants, research has demonstrated that those with large genomes are at greater risk of extinction, are less adapted to living in polluted soils and are less able to tolerate extreme environmental conditions – all highly relevant in today’s changing world,” says Kew. According to biologists, many desert plants have small genomes, enabling them to grow rapidly after a rain.
No one really knows why some organisms have such large genomes—before Paris japonica's genome was measured, the record holder was Protopterus aethiopicus, a bottom-dwelling fish. The size of a genome doesn't correlate with the complexity of the organism—while some DNA codes for identifiable traits, such as color and size, other DNA doesn't seem to code for anything. Geneticists are researching why some organisms carry so much non-coding DNA—perhaps Paris japonica will shed some light.
Anna Laurent is a writer and photographer. Her work explores how we look at plants, and how those plants behave.