Eleusine Gaertn.
Eleusine is a small genus of nine species, eight in Africa and one in South America. Evidently, none is native in Belgium but several have been recorded as (usually) ephemeral aliens.
The distinction of the Belgian representatives of the genus Eleusine is not always straightforward and some diacritic features are not easily integrated in an identification key. Moreover, many characteristics are more or less variable and merely quantitative and systematic treatments in various floras are sometimes very deviating or even conflicting (see under the species accounts). Most of the widespread taxa seem to intergrade.
The taxonomic treatment of the taxa closely related to Eleusine indica considerably changed in recent times as a result of chloroplast DNA analysis: Eleusine indica subsp. africana has first been transferred to E. coracana (as subsp. africana) (compare Phillips 1972, Hilu & Johnson 1997, Hilu 2003). The latest molecular data, however, suggest that E. africana, E. coracana and E. indica are in fact distinct species (Peterson & al. 2015). Given these changed taxonomic insights further studies will be required to assess the exact identity of members of this species complex in Belgium. For now, the taxonomic framework proposed by Hilu (2003) is here applied.
1 Perennial grasses (but often flowering in the first year!), prostrate to ascending (usually less than 25 cm tall). Inflorescence usually digitate with 2-3 (rarely 4) branches, these oblong, 20-35 mm long === 3. Eleusine tristachya
1 Annual grasses, ascending to erect. Inflorescence often subdigitate (with one branch attached immediately below the terminal whorl) with (2-) 3 to numerous branches, these mostly linear and at least 30 mm long (if oblong than habit always erect and more than 25 cm tall) === 2
2 Lower glume 2- or 3-veined. Panicle braches 5-15 mm wide. Surface of the seeds granular to nearly smooth === 1. E. coracana
2 Lower glume 1-veined. Panicle branches 3-5 mm wide. Surface of the seeds striate === 2. E. indica
References:
Jansen P. (1951) Flora Neerlandica, deel 1, aflevering 2. KNBV, Amsterdam: 272 p.
Hilu K.W. (2003) Eleusine. In: Barkworth M.E. & al. (eds.), Flora of North America north of Mexico, vol. 25. Oxford University Press, New York-Oxford: 109-110.
Hilu K.W. & Johnson J.L. (1997) Systematics of Eleusine Gaertn. (Poaceae, Chloridoideae): Chloroplast DNA and total evidence. Ann. Missouri Bot. Gard. 84: 841-847.
Liu Q. & Peterson P.M. (2010) Advances in systematics of adaptively radiated Eleusine Gaertn. (Poaceae) (in Chinese). Journ. Trop. Subtrop. Bot. 18(3): 335-342.
Lye K.A. (1999) Nomenclature of finger millet (Poaceae). Lidia 4(5): 149-152.
Nightingale M.E. & Weiller C.M. (2005) Eleusine. In: Mallett K. (ed.), Flora of Australia, vol. 44B, Poaceae 3: 416-418. Australian Biological Resources Study, Canberra.
Peterson P.M., Romaschenko K. & Arrieta Y.H. (2015) A molecular phylogeny and classification of the Eleusininae with a new genus, Micrachne (Poaceae: Chloridoideae: Cynodonteae). Taxon 64(3): 445-467. [available online at: https://www.researchgate.net/publication/271851457_A_molecular_phylogeny_and_classification_of_the_Eleusininae_with_a_new_genus_Micrachne_%28Poaceae_Chloridoideae_Cynodonteae%29]
Phillips S.M. (1972) A survey of the genus Eleusine Gaertn. (Gramineae) in Africa. Kew Bull. 27: 251-270.
Stace C. (2010) New flora of the British Isles, 3th ed.: XXXII + 1232 p. Cambridge University Press.