Largest angiosperm genome

The largest genome (i.e., total amount of DNA in the nucleus of a cell) for an angiosperm (flowering plant) assessed to date using best-practice methods is 149 billion base pairs (Gbp, or gigabases) for the Japanese woodland plant Paris japonica, as reported by botanists from the Royal Botanic Gardens, Kew (UK) in the Botanical Journal of the Linnean Society in September 2010. This plant boasts over 46 times more genetic material than that found in human cells (3.2 Gbp).

At the time, this also gave Paris japonica the largest genome for any eukaryote organism overall. This has since been surpassed by the Tmesipteris oblanceolata fork fern, native to New Caledonia and other nearby Pacific islands, which has a 160.45-Gbp genome, as revealed in iScience on 31 May 2024.

To determine genome size, the most common technique that scientists employ is “flow cytometry”. This involves first isolating nuclei and staining them with a fluorescent dye that binds quantitatively to the amount of DNA present in each nucleus. The suspended nuclei are then loaded onto the flow cytometer and as they pass through a laser beam the amount of fluorescent light is measured (the bigger the genome, the more fluorescent light is detected by the flow cytometer). As well as the number of base pairs, genome size can also be expressed as a weight in picograms (one-trillionth of a gram): the total DNA of P. japonica weighs in at 152 picograms.

At the other end of the scale, the smallest known genome for an angiosperm is that of the carnivorous Genlisea tuberosa, a corkscrew plant endemic to Brazil. According to a study published in the Annals of Botany in December 2014, this plant has a mere 61 megabase pairs (or 61 million base pairs).

The largest plant genome to have been sequenced and assembled, which involves not just measuring the total amount of DNA but reconstructing it into its original order, is for the European mistletoe (Viscum album) for which 94 Gbp has so far been curated by scientists from the Darwin Tree of Life project as reported in December 2022.