Aconogonon Reichenb.
As usually circumscribed (after exclusion of Rubrivena) Aconogonon counts ca. 25 species (Galasso & al. 2009). However, the genus is difficult to separate from Koenigia L. on morphological grounds. Recent molecular studies support merging both genera since Koenigia was shown to be nested in Aconogonon (Galasso & al. 2009, Schuster & al. 2015). Likewise, Rubrivena is also better merged with these two genera. For nomenclatural reasons, the generic name Koenigia has priority and the necessary transfers were already provided (Schuster & al. l.c.). Pending further studies, however, a more conservative approach is adopted in this account. Some species are cultivated as ornamentals (see for instance Reiersen 2000, Jäger & al. 2008, Stace 2010) but the genus appears to be rare in cultivation in Belgium.
Aconogonon is still insufficiently understood. Molecular data showed that some species with multiple accessions were not monophyletic, for instance the cultivated ornamentals A. campanulatum and A. molle (Schuster & al. 2015).
The genus is often referred to as “Aconogonum” (e.g. Galasso & al. 2006). However, the original spelling is 'Aconogonon' and this spelling was recently conserved (Applequist 2016).
1. Leaf blade narrowly lanceolate, 4-20x as long as wide. Lower leaf surface glabrous (except margins) === Aconogonon divaricatum
1. Leaf blade broadly ovate, less than 3x as long as wide. Lower leaf surface hairy all over === 2
2. Tepals pink or reddish, fused for ½-1/4 their length === A. campanulatum
2. Tepals white, free to base === A. xfennicum
Literature:
Applequist W.L. (2016) Report of the Nomenclature Committee for Vascular Plants: 67. Taxon 65(1): 169-182. [available online at: http://www.ingentaconnect.com/contentone/iapt/tax/2016/00000065/00000001...
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.
Galasso G., Colatore A. & Kleih M. (2006) Notula 1246. In: Scoppola A. (ed.), Notulae alla checklist della flora vascolare italiana, 2 (1192-1266). Inform. Bot. Ital. 38(1): 206-207.
Hong S.-P. (1992) Taxonomy of the genus Aconogonon (Polygonaceae) in Himalaya and adjacent regions. Symb. Bot. Upsal. 30(2): 1-118.
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.
Li A.-J., Bao B.-J., Grabovskaya-Borodina A.E., Hong S.P., McNeill J., Mosyakin S.L., Ohba H. & Park C.W. (2003). Polygonum. In: Wu Z.Y., Raven P.H. & Hong D.Y. (eds.), Flora of China, vol. 5. Science Press, Beijing, and Missouri Botanical Press, St. Louis: 75-78. [available online at: http://flora.huh.harvard.edu/china//PDF/PDF05/Polygonum.pdf]
Reiersen J. (2000) Aconogonon. In: Jonsell B. (ed.), Flora Nordica, vol. 1. The Bergius Foundation, Stockholm: 236-240.
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_...
Stace C. (2010) New flora of the British Isles, 3th ed.: XXXII + 1232 p. Cambridge University Press.