Reynoutria is a genus of robust, erect perennial flowering plants in the family Polygonaceae (the knotweed or buckwheat family), placed within the order Caryophyllales. The genus comprises a small number of species native to eastern China, Eastern Asia, and the Russian Far East, though several members have been introduced — and have become highly invasive — across Europe and North America.
Plants in Reynoutria grow from spreading rhizomes and are typically monoecious, bearing mostly bisexual flowers alongside some unisexual ones. The petals are dry and papery at maturity, and the fruits are three-edged achenes. Flowers are arranged in panicles and bear separated triangular stigmas with fringed (fimbriate) margins on long divided styles.
The genus was erected by Dutch botanist Maarten Houttuyn in 1777, originally for the species now known as Reynoutria japonica (Japanese knotweed). Its taxonomic history has been contentious: the genus has been repeatedly merged with and separated from the closely related genus Fallopia, with competing arguments grounded in morphology, plant habit, and chemistry. Modern molecular phylogenetic studies have resolved these debates, establishing Reynoutria as a well-supported monophyletic group within the tribe Polygoneae of subfamily Polygonoideae. Within that tribe it forms the "RMF clade" together with Muehlenbeckia and Fallopia s.s., all three sharing the trait of extra-floral nectaries.
The most ecologically significant members include R. japonica (Japanese knotweed) and the hybrid R. × bohemica (R. japonica × R. sachalinensis), which rank among the world's most problematic invasive plants in temperate regions.
Etymology
The genus name Reynoutria was coined by Dutch botanist Maarten Houttuyn in 1777 when he described the type species R. japonica. It was named in honour of "Herr von Reynoutre," a person reported to have rendered great service to botany.
Distribution
Reynoutria is native to eastern China, broader Eastern Asia, and the Russian Far East. Several species — most notably R. japonica and the hybrid R. × bohemica — have been introduced to Europe and North America, where they have naturalised extensively and are considered highly invasive.
Ecology
Members of Reynoutria grow from deep, spreading rhizomes that enable rapid vegetative spread and make eradication difficult. Reynoutria japonica and the hybrid R. × bohemica are among the most aggressive invasive plants in temperate Europe and North America, outcompeting native vegetation, altering soil chemistry, and persisting despite repeated cutting.
Taxonomy Notes
The genus was long taxonomically unstable due to repeated mergers with and separations from Fallopia. The confusion began as early as 1856–57, when Carl Meissner grouped Reynoutria with Fallopia in Polygonum sect. Tiniaria, and continued through the late 20th century. Molecular phylogenetic studies have since confirmed Reynoutria as a well-supported monophyletic taxon, placed in tribe Polygoneae of subfamily Polygonoideae, most closely related to Muehlenbeckia and Fallopia s.s. in the "RMF clade."
