Bistorta (L.) Scop.
Recent molecular phylogenetic research (Galasso & al. 2009) confirms the generic status of Bistorta. According to Schuster & al. (2015) it is closer to Aconogonon than it is to Persicaria. It is a genus of ca. 50 species, mostly native to arctic and temperate regions of Eurasia and North America. One species is native in Belgium as well, Bistorta officinalis Delarbre (syn.: Polygonum bistorta L.). Several species are more or less widely cultivated as ornamentals, especially Bistorta affinis (D. Don) Greene (syn.: Polygonum affine D. Don) and B. amplexicaulis (see also Jäger & al. 2008 for additional species).
1. Upper leaves clasping stem. Stem erect, usually branched. Flowers intensely red === Bistorta amplexicaulis
1. Leaves not clasping stem. Stem creeping or ascending to more or less erect, branched or not. Flowers pale pink, more rarely reddish === 2
2. Evergreen and matforming perennial with prostrate stems. Lowermost leaves with unwinged petioles === B. affinis
2. Perennial with ascending to more or less erect stems, dying down in winter. Lowermost leaves with petioles distinctly winged in upper part (native) === B. officinalis
Literature:
Galasso G., Banfi E., De Mattia F., Grassi F., Sgorbati S. & Labra M. (2009) Molecular phylogeny of Polygonum L. s.l. (Polygonoideae, Polygonaceae), focusing on European taxa: preliminary results and systematic considerations based on rbcL plastidial sequence data. Atti Soc. It. Sci. Nat. Museo Civ. Stor. Nat. Milano 150(1): 113-148.
Jäger E.J., Ebel F., Hanelt P. & Müller G. (eds.) (2008) Rothmaler Band 5. Exkursionsflora von Deutschland. Krautige Zier- und Nutzpflanzen. Springer Verlag, Berlin: 880 p.
Kim S. & Donoghue M.J. (2008) Molecular phylogeny of Persicaria (Persicarieae, Polygonaceae). Syst. Bot. 33(1): 77-86.
Schuster T.M., Reveal J., Bayly M. & Kron K.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. [available online at: https://www.researchgate.net/publication/288889005_An_updated_molecular_...