Gentianaceae is a family with more than 80 genera and probably more than 1600 species (Mabberley 2008). Generic boundaries for its representatives in western Europe are straightforward now. Six genera are accepted as native in Belgium: Blackstonia Huds., Cicendia Adans., Centaurium Hill, Gentiana L., Gentianella Moench and Gentianopsis Ma. The latter genus, that comprises the ‘fringed gentians’ (Ma 1951), was not yet segregated from Gentianella by Lambinon & Verloove (2012) but its generic status is corroborated by the molecular phylogenetic studies of Yuan & Kupfer (1995). Its use at generic level has become widely accepted now (e.g. van der Meijden 2005, Stace 2010, Tison & de Foucault 2014) and is also applied here.
Identity and status of Blackstonia is somewhat unclear in Belgium. The ‘usual’ species surely is B. perfoliata (L.) Huds. (e.g. Lambinon & Verloove 2012). The very similar B. acuminata (Koch & Ziz) Domin (syn.: B. perfoliata subsp. serotina (Koch ex Reichenb.) Vollm.) was known from the southernmost parts of the Netherlands, close to the Belgian frontier (van der Meijden 2005). Since 2008 it has also been recorded from sand raised sites in the Waaslandhaven in Belgium. These records possibly can be accepted as natural range extensions. Both taxa are not always easily told apart and their taxonomic rank is debated, although plants with intermediate features are not found (Tison & de Foucault 2014).
1 Style filiform. Corolla pink or yellow (if yellow, then stem slender and flowers not crowded in axillary and terminal cymes) (native) === Blackstonia, Centaurium and Cicendia
Style short or absent, stigmas subsessile on fruit. Corolla purple to blue (rarely white) or yellow (if yellow, then stem robust and flowers numerous in leaf axils) === 2
2 Corolla not ciliate, with appendages between the lobes === Gentiana
Corolla ciliate (either at base on inner side or along sides), without appendages (native) === Gentianella and Gentianopsis
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Ma Y.C. (1951) Gentianopsis: a new genus of Chinese Gentianaceae. Acta phytotaxonomica Sinica 1: 5-19.
Mabberley D.J. (2008) Mabberley’s plant-book (3th ed.). Cambridge University Press, Cambridge: XVIII + 1021 p.
Rybczyński J.J., Davey M.R. & Mikula A. (eds.) (2014) The Gentianaceae - Volume 1: Characterization and Ecology. Springer.
Stace C. (2010) New flora of the British Isles, 3th ed.: XXXII + 1232 p. Cambridge University Press.
Struwe L. & Albert V.A. (eds.) (2002) Gentianaceae: systematics and natural history. Cambridge University Press, Cambridge: x + 652 p.
Tison J.-M. & de Foucault B. (coord.) 2014) Flora Gallica. Flore de France. Editions Biotope, Mèze : xx + 1196 p.
Tutin T.G. (1972) Gentianaceae. In: Tutin T.G. & al. (eds.), Flora Europaea, vol. 3. Cambridge University Press: 56-67.
Van der Meijden R. (2005) Heukels’ Flora van Nederland (23e druk). Wolters-Noordhoff, Groningen: 685 p.
Yuan Y.M. & Kupfer P. (1995) Molecular phylogenetics of the subtribe Gentianinae (Gentianaceae) inferred from the sequences of internal transcribed spacers (ITS) of nuclear ribosomal DNA. Plant Systematics and Evolution 196: 207-226.
Yuan Y.M. & Kupfer P. & Doyle J.J. (1996): Infrageneric phylogeny of the genus Gentiana (Gentianaceae) inferred from nucleotide sequences of the internal transcribed spacers (ITS) of nuclear ribosomal DNA. Amer. J. Bot. 83(5): 641-652.