Paris japonica is the flowering plant with the largest known nuclear genome, containing about 149 billion base pairs.
Paris japonica is a herbaceous species in the family Melanthiaceae, native to Japan. Its enormous genome is measured as nuclear DNA, the genetic material stored in the cell nucleus. Genome size is not the same as organismal complexity: a plant with more DNA does not necessarily have more genes or greater biological complexity.
The species has a haploid genome size of roughly 152.23 gigabases in widely cited estimates, equivalent to about 149 billion base pairs. This is many times larger than the human haploid genome. Large genomes can affect cell size, growth rate, and ecological strategy, although the causes and consequences vary among plants.
Paris japonica is sometimes confused with Paris polyphylla, a related medicinal plant. It is also distinct from the best-known genome-sequenced model plant, Arabidopsis thaliana, whose genome is comparatively small and was completed much earlier.