Herb Paris
Paris species stand out among garden plants. Their unmistakable, fly-pollinated flowers consist of a spherical, purple-black ovary surrounded by large yellow stamens, a whorl of reduced, almost filamentous petals – the least conspicuous part of the whole – and a final whorl of leaf-like sepals. The ovary eventually develops into a glossy, berry-like capsule.
The genus contains around 30 species, of which Paris quadrifolia and Paris polyphylla are those most often found in cultivation. Most monocotyledons have strap-like leaves with parallel veins. In contrast, Paris species have oval or diamond-shaped leaves with net-like venation, arranged in rings (whorls) around the stem. As the names suggest, Paris quadrifolia bears leaves in groups of four, while Paris polyphylla has numerous leaves in each whorl on the stem.
The centre of species diversity in the genus is China, but its range extends across temperate areas of Asia and Europe. Paris quadrifolia is native to Britain, and while not widespread, is locally common in some areas, including at least one site around Oxford. It is a perennial species of ancient woodland on moist, calcareous, humus-rich soil in dappled shade. Paris quadrifolia and Paris polyphylla are easily grown in gardens, where they can be propagated by seed or division, make eye-catching, summer-flowering additions to a shady border.
Within the genus Paris we find a celebrity of genetics. In 2010, Paris japonica was found to have the largest known genome of any organism. Genome size, the amount of DNA a species has in the nucleus of each of its cells, varies widely within and among different groups of organisms. The Paris japonica genome contains 149 billion nucleotide base pairs, 15% more than the next organism – a species in a genus (Trillium) related to Paris – with 130 billion base pairs. The smallest known flowering plant genome, with approximately 64 million base pairs, is found in the Brazilian insectivorous plant, Genislea aurea. For comparison, humans have a genome size of about 3.2 billion base pairs.
One practical consequence of cells with large genomes is that they are likely to divide more slowly than cells with small genomes. Slow cell division may prolong an organism’s life cycle, making it slower to reproduce and adapt, and perhaps less resilient to changing environmental conditions. Such plants are likely to grow slowly, survive only in stable environments and therefore be at a greater risk of extinction than rapidly growing species found in changing environments.
Further reading
Cunningham AB et al. 2018. Paris in the spring: A review of the trade, conservation and opportunities in the shift from wild harvest to cultivation of Paris polyphylla (Trilliaceae). Journal of Ethnopharmacology 222: 208-216.
Jacquemyn H et al. 2008. Biological Flora of the British Isles: Paris quadrifolia L. Journal of Ecology 96: 833-844.
Pellicer J et al. 2014. A universe of dwarfs and giants: genome size and chromosome evolution in the monocot family Melanthiaceae. New Phytologist 201: 484-497.
Ruth Calder