(incl. Monolepis Schrad.)
Blitum, as currently understood (see Fuentes-Bazan & al. 2012, is a segregate genus of Chenopodium and counts 13 species in the Old and New World. One is native in Belgium, Blitum bonus-henricus (L.) Reichenb. (syn.: Chenopodium bonus-henricus L.). Molecular studies (Fuentes-Bazan & al. l.c.) demonstrated that species of Blitum are in fact more closely related to Spinacia than they are to the remainder of Chenopodium s.l. Blitum bonus-henricus looks rather different but is obviously closely related to B. virgatum. A hybrid between both species has been reported by Melzer (1987).
Monolepis used to be a small genus of three to five species, distributed in temperate western North America, Central and northeastern Asia and southern South America. However, Fuentes-Bazan & al. (2012) demonstrated that it is nested in Blitum. See also Sukhorukov & al. (2018).
1. Perianth segments usually 1 (or up to 3 in some flowers). Stamens 1 or 2, sometimes absent === Blitum nuttallianum
1. Perianth segments 5. Stamens usually 5 === 2
2. Perianth red and fleshy at maturity. Annual. Leaf blade variable but not as above. Stigmas short, rarely exceeding 0,8 (-1) mm === 3
2. Perianth not red and fleshy at maturity. Rhizomatous perennial. Leaf blade triangular with nearly entire margins. Stigmas elongated, up to 2 mm long (native) === B. bonus-henricus
3. Inflorescence bracteate to apex === B. virgatum
3. Inflorescence ebracteate in apical part === B. capitatum
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://docserver.ingentaconnect.com/deliver/connect/bgbm/05119618/v42n1/s1.pdf?expires=1344851590&id=70034238&titleid=75004866&accname=National+Botanical+Garden+of+Belgium&checksum=6DCE49C10B29A7C8720D5973C560C22A]
Melzer H. (1987) Chenopodium bonus-henricus x foliosum = Ch. x tkalcsicsii Melzer hybr. nov. - eine neue Hybride zweier sehr unterschiedlicher Arten. Berichte der Bayerischen Botanischen Gesellschaft 58: 73-77.
Sukhorukov A.P., Nilova M.V., Krinitsina A.A., Zaika M.A., Erst A.S. & Shepherd K.A. (2018) Molecular phylogenetic data and seed coat anatomy resolve the generic position of some critical Chenopodioideae (Chenopodiaceae – Amaranthaceae) with reduced perianth segments. PhytoKeys 109: 103-128. [available online at: https://phytokeys.pensoft.net/article/28956/list/9/]