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Reynoutria
Japanese knotweed, Reynoutria japonica
Scientific classification
Kingdom:	Plantae
Clade:	Tracheophytes
Clade:	Angiosperms
Clade:	Eudicots
Order:	Caryophyllales
Family:	Polygonaceae
Subfamily:	Polygonoideae
Genus:	Reynoutria Houtt.

Reynoutria is a genus of flowering plants in the Polygonaceae, also known as the knotweed or buckwheat family. The genus is native to eastern China, Eastern Asia and the Russian Far East, although species have been introduced to Europe and North America. Members of the genus, including R. japonica (Japanese knotweed) and its hybrid with R. sachalinensis, are highly invasive plants.

Description

Species placed in the genus Reynoutria are robust erect perennial plants, growing from rhizomes. They are usually monoecious, with mostly bisexual flowers, but also some unisexual flowers. The petals of the flowers are dry and paperlike when mature. The fruits are achenes with threefold sharp edges. The inflorescence is in the form of a panicle. The flowers have separated triangular stigmas with fringes (fimbriate) borne on long divided styles.

Taxonomy

The genus Reynoutria was erected by Maarten Houttuyn in 1777 for the species R. japonica. It was named in honour of Herr von Reynoutre who had been reported to have done a great deal of service to botany. As with many species in the family Polygonaceae, the taxonomic boundaries of Reynoutria have been much confused; in particular, it has been repeatedly merged with and separated from Fallopia. This reorganization began in 1856 or 1857, when Carl Meissner grouped Reynoutria together with Fallopia in Polygonum sect. Tiniaria Meisn. and continued through to the late 20th century, with competing arguments based around plant morphology, habit and chemistry. A series of molecular phylogenetic studies have clarified these relationships; Reynoutria is a well-supported monophyletic taxon.

Reynoutria is placed in the tribe Polygoneae of the subfamily Polygonoideae. Within the tribe, it is most closely related to the genera Muehlenbeckia and Fallopia s.s., forming the so-called "RMF clade". While Muehlenbeckia and Fallopia s.s. are believed to be more closely related, all three share the morphological character of extra floral nectaries.

Species

As of August 2024, Plants of the World Online recognized the following species:

• Reynoutria ciliinervis (Nakai) Moldenke
• Reynoutria compacta (Hook.f.) Nakai
• Reynoutria forbesii (Hance) T.Yamaz.
• Reynoutria japonica Houtt. – Asian knotweed, Japanese knotweed
• Reynoutria multiflora (Thunb.) Moldenke – Chinese knotweed
• Reynoutria sachalinensis (F.Schmidt) Nakai – giant knotweed, Sakhalin knotweed
• Reynoutria × bohemica Chrtek & Chrtková – Bohemian knotweed
• Reynoutria × moravica (Hodálová & Mereďa) Olshanskyi & Antonenkoi

Invasive potential

All members of the RMF clade appear to have the potential to become invasive, in some cases via vigorous hybrids. Reynoutria japonica is highly invasive throughout Europe and North America. The hybrid between R. japonica and R. sachalinensis, R. × bohemica, is also invasive, particularly in North America. R. japonica hybridizes with the New Zealand Muehlenbeckia australis. (The related M. complexa has established populations in southern parts of Britain and in the Channel Islands.)

References

1. ^ "Reynoutria Houtt.", Plants of the World Online, Royal Botanic Gardens, Kew, retrieved 2019-02-25
2. ^ Schuster, T.M.; Wilson, K.L. & Kron, K.A. (2011), "Phylogenetic relationships of Muehlenbeckia, Fallopia and Reynoutria (Polygonaceae) investigated with chloroplast and nuclear sequence data", International Journal of Plant Sciences, 172 (8): 1053–1066, doi:10.1086/661293, JSTOR 10.1086/661293, S2CID 84015547
3. "Plant Name Details for Reynoutria Houtt.", The International Plant Names Index, retrieved 2019-03-03
4. Houttuyn, M (1777) , "Reynoutria", Natuurlyke historie of Uitvoerige beschryving der dieren, planten, en mineraalen, vol. 2, pp. 639–640, retrieved 2019-03-03
5. ^ Schuster, Tanja M.; Reveal, James L.; Bayly, Michael J. & Kron, Kathleen A. (2015), "An updated molecular phylogeny of Polygonoideae (Polygonaceae): Relationships of Oxygonum, Pteroxygonum, and Rumex, and a new circumscription of Koenigia", Taxon, 64 (6): 1188–1208, doi:10.12705/646.5
6. Desjardins, Stuart D.; Bailey, John P.; Zhang, Baowei; Zhao, Kai; Schwarzacher, Trude (2023-02-27). "New insights into the phylogenetic relationships of Japanese knotweed (Reynoutria japonica) and allied taxa in subtribe Reynoutriinae (Polygonaceae)". PhytoKeys (220): 83–108. doi:10.3897/phytokeys.220.96922. ISSN 1314-2003. PMC 10209619. PMID 37251615.
7. DECRAENE, LOUIS-PHILIPPE RONSE; AKEROYD, J. R. (December 1988). "Generic limits in Polygonum and related genera (Polygonaceae) on the basis of floral characters". Botanical Journal of the Linnean Society. 98 (4): 321–371. doi:10.1111/j.1095-8339.1988.tb01706.x. ISSN 0024-4074.
8. Sanchez, A.; Schuster, T.M. & Kron, K.A. (2009), "A largescale phylogeny of Polygonaceae based on molecular data", International Journal of Plant Sciences, 170 (8): 1044–1055, doi:10.1086/605121, S2CID 84694521
9. Sanchez, A.; Schuster, T.M.; Burke, J.M. & Kron, K.A. (2011), "Taxonomy of Polygonoideae (Polygonaceae): A new tribal classification", Taxon, 60 (1): 151–160, doi:10.1002/tax.601013, JSTOR 41059829
10. Schuster, T.M.; Reveal, J.L. & Kron, K.A. (2011), "Evolutionary Relationships within Polygoneae (Polygonaceae: Polygonoideae)", Taxon, 60: 1653–1666, doi:10.1002/tax.606010, cited in Schuster et al. (2015)
11. Fan, D.-M.; Chen, J.-H.; Meng, Y.; Wen, J.; Huang, J.-L. & Yang, Y.-P. (2013), "Molecular phylogeny of Koenigia L. (Polygonaceae: Persicarieae): Implications for classification, character evolution and biogeography.", Molecular Phylogenetics and Evolution, 69 (3): 1093–1100, Bibcode:2013MolPE..69.1093F, doi:10.1016/j.ympev.2013.08.018, PMID 23994356
12. "Reynoutria Houtt. | Plants of the World Online | Kew Science". Plants of the World Online. Retrieved 2024-08-19.

• Polygonoideae
• Polygonaceae genera