Oxybasis Kar. et Kir.
Oxybasis, as currently understood (see Fuentes-Bazan & al. 2012, Sukhorukov & al. 2013, Sukhorukov & Zhang 2013) is a segregate genus of Chenopodium and counts five or more species in the Old and New World, all related to C. rubrum. Four are native in Belgium, Oxybasis chenopodioides (L.) S. Fuentes, Uotila & Borsch (syn.: Blitum chenopodioides L., Chenopodium chenopodioides (L.) Aellen), O. glauca (L.) S. Fuentes, Uotila & Borsch (syn.: Chenopodium glaucum L.), O. rubra (L.) S. Fuentes, Uotila & Borsch (syn.: Chenopodium rubrum L.) and O. urbica (L.) S. Fuentes, Uotila & Borsch (syn.: Chenopodium urbicum L.). The latter is possibly extinct now as a genuinely native species in Belgium (or at least very rare) but is still sometimes seen as an introduction, mostly with cereals, in port areas. Representatives of this genus are distinguished by often dimorphic flowers (with horizontal as well as vertical seeds), usually (1-)2-3 stamens (always 5 in Chenopodium s.str.), glabrous or nearly glabrous foliage, etc. Oxybasis urbica obviously is less typical and, morphologically, seems closer to Chenopodiastrum but its placement in Oxybasis is justified by molecular data (Fuentes-Bazan & al. 2012, Sukhorukov & al. 2013).
1. Most flowers with 3 tepals and vertical seeds (only terminal flowers with 5 tepals and horizontal seeds) === 2
1. All flowers with 5 tepals and horizontal seeds (native) === Oxybasis urbica
2. Leaves green above, glaucous beneath, not succulent === O. glauca (incl. var. salina)
2. Leaves green (or reddish) on both sides, succulent (native) === C. chenopodioides and C. rubrum
Additional alien: Oxybasis macrosperma (Hook. f .) S. Fuentes, Uotila & Borsch (syn. : Chenopodium macrospermum Hook. f. (S-Am., wool alien).
Fuentes-Bazan S., Uotila P. & Borsch T. (2012) A novel phylogeny-based generic classification for Chenopodium sensu lato, and a tribal rearrangement of Chenopodioideae (Chenopodiaceae). Willdenowia 42(1): 5-24. [available online at: http://www.ingentaconnect.com/content/bgbm/will/2012/00000042/00000001/art00001]
Sukhorukov A.P., Uotila P., Zhang M., Zhang H.-X., Speranskaya A.S. & Krinitsyna A.A. (2013) New combinations in Asiatic Oxybasis (Amaranthaceae s.l.): evidence from morphological, carpological and molecular data. Phytotaxa 144(1): 1-12. [available online at: http://biotaxa.org/Phytotaxa/article/viewFile/phytotaxa.144.1.1/5422]
Sukhorukov A.P. & Zhang M. (2013) Fruit and Seed Anatomy of Chenopodium and Related Genera (Chenopodioideae, Chenopodiaceae/Amaranthaceae): Implications for Evolution and Taxonomy. Plos One 8(4): 1-18. [available online at: http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0061906]
Verloove F. (2013) A new combination in Oxybasis (Amaranthaceae). New Journ. Bot. 3(1): 59-60.