Ranunculus L.
As currently understood Ranunculus is a large genus with about 600 species that are predominantly distributed in the temperate regions of the world (Mabberley 2008). As a result of recent molecular phylogenetic studies its boundaries have slightly changed and these changes partly affect western European taxa. The native species Ranunculus ficaria L. now belongs in the segregate genus Ficaria (as F. verna Huds.) (Emadzade & al. 2010) and this taxonomy is now widely accepted (e.g. Stace 2010). Ranunculus subgenus Batrachium (DC.) A. Gray, on the contrary, should be maintained in Ranunculus s.str. Eleven species of subgenus Ranunculus and ten species of subgenus Batrachium are native in Belgium (Lambinon & Verloove 2012), although some now are very rare or even extinct. One species, Ranunculus arvensis L., is usually accepted as a native species but it is at most an archaeophyte. Moreover, nowadays it is almost exclusively seen as an (ephemeral) alien in port areas. About 30-40 species are cultivated as ornamentals in Europe (Leslie 1989, Jäger & al. 2008) but only relatively few are more or less widespread in cultivation. One out of these, the very rare native species Ranunculus lingua L., is increasingly planted in pond margins and sometimes escapes. As a result its genuine, wild distribution has become obscure.
1 Petals white (native) === Ranunculus subgenus Batrachium and R. platanifolius
Petals yellow === 2
2 Leaves entire or merely toothed (native) === R. flammula and R. lingua
Leaves distinctly lobed or divided === 3
3 Plant perennial, stem decumbent or creeping, rooting at nodes (stoloniferous) (native) === R. repens
Plant annual or perennial, with erect, non-rooting stems === 4
4 Achenes numerous (40-300), at most 1,2 mm across (native) === R. sceleratus
Achenes usually less than 40, at least (1,8-) 2 mm across === 2
5 Face of achene tuberculate (sometimes near margin only) to spiny. Plant always annual === 6
Face of achene perfectly smooth. Plant perennial or (rarely) annual === 10
6 Sepals spreading at anthesis, not reflexed. Face of achene with conspicuous spines up to 3 mm long (native) === R. arvensis
Sepals reflexed at anthesis. Face of achene tuberculate or echinate, not spiny === 7
7 Receptacle glabrous. Petals 2-3 mm long === R. parviflorus
Receptacle hairy. Petals usually longer === 8
8 Beak of achene 0,3-0,5 (-0,7) mm long. Face of achene tuberculate (often only sparsely so or near margin only) === 9
Beak of achene 2-3 mm long. Face of achene covered with spines === R. muricatus
9 Petals 6-10(-14) mm long, twice as long as sepals. Face of achene sparsely tuberculate (margin only). Anthers 1,2-1,8 mm long. Basal leaves usually compound (native) === R. sardous
Petals 2-6 mm long, ca. as long as sepals. Face of achene entirely covered with tubercles. Anthers 0,6-1,2 mm long. Basal leaves lobed, rarely compound === R. trilobus
10 Petals 2-4 mm long, not exceeding sepals. Plant annual (rarely short-lived perennial) === 11
Petals at least 8 mm long, distinctly longer than sepals. Plant perennial (native) === R. acris, R. auricomus, R. bulbosus and R. serpens
11 Stem hispid. Basal leaves trifoliolate, leaflets deeply cleft with acute segments. Petals 2-4 mm long. Receptacle elongated at maturity, 9-12 mm long. Beak of achene 0,6-0,8 mm long === R. pensylvanicus
Stem sparsely pilose. Basal leaves undivided or shallowly 3-lobed, leaflets crenate or dentate with rounded segments. Petals 4-5 mm long. Receptacle hemispheric to globose at maturity, ca. 5 mm long. Beak of achene 0,8-1 mm long === R. marginatus
Additional aliens: Ranunculus gramineus L. (W-Medit., garden escape?) and R. lanuginosus L. (garden escape).
Literature:
Benson L.D. (1948) A treatise on the North American Ranunculi. Amer. Midl. Naturalist 40: 1-261.
Benson L.D. (1954) Supplement to a treatise on the North American Ranunculi. Amer. Midl. Naturalist 52: 328-369.
Cook C.D.K, Grau J. & López Gonzales G. (1986). Ranunculus. In: Castroviejo S. & al. (eds.), Flora Iberica 1. Lycopodiaceae to Papaveraceae. CSIC. Real Jardín Botánico. Madrid.
Emadzade K. (2010) Molecular phylogeny, evolution and biogeography of Ranunculus (Ranunculaceae) and related genera. Dissertation Universität Wien. [available online at: http://othes.univie.ac.at/9371/1/2010-02-02_0549709.pdf]
Emadzade K., Lehnebach C., Lockhart P. & Hörandl E. (2010) A molecular phylogeny, morphology and classification of genera of Ranunculeae (Ranunculaceae). Taxon 59: 809-828.
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.
Lambinon J. & Verloove F. (avec coll. Delvosalle L., Toussaint B., Geerinck D., Hoste I., Van Rossum F., Cornier B., Schumacker R., Vanderpoorten A. & Vannerom H.) (2012) Nouvelle Flore de la Belgique, du Grand-Duché de Luxembourg, du Nord de la France et des Régions voisines (Ptéridophytes et Spermatophytes). Sixième édition. Jardin botanique national de Belgique, Meise: CXXXIX + 1195 p.
Lawalrée A (1955) Ranunculaceae. In: Robyns W. (ed.), Flore Générale de Belgique, vol. 2, fasc. 1. Jardin Botanique de l’Etat, Bruxelles: 13-114.
Leslie A.C. (1989) Ranunculus. In: Walters S.M. & al. (eds.), The European Garden Flora, vol. 3. Cambridge University Press, Cambridge: 364-368.
Mabberley D.J. (2008) Mabberley’s plant-book (3th ed.). Cambridge University Press, Cambridge: XVIII + 1021 p.
McKelvie A. (1986) The genus Ranunculus, part 2. European species. J. Scott. Rock Gard. Club 20: 64-83. [available online at: http://files.srgc.net/journals/vol_1%20to_113/79.pdf]
Srivastava S.K. (2010) Revision of Genus Ranunculus L. (Ranunculaceae) in India. Taiwania 55(3): 273-314. [available online at: http://tai2.ntu.edu.tw/taiwania/pdf/tai.2010.55.3.273.pdf]
Stace C. (2010) New flora of the British Isles, 3th ed.: XXXII + 1232 p. Cambridge University Press.
Tutin T.G. & Akeroyd J.R. (1993) Ranunculus L. In: Tutin T.G. & al. (eds.), Flora Europaea, volume 1 (2nd ed.). Cambridge University Press: 269-286.
Uotila P. (2001) Ranunculaceae. In: Jonsell B. (ed.), Flora Nordica, vol. 2. The Bergius Foundation, Stockholm: 227-335.
Wang W. & Gilbert M.G. (2001) Ranunculus. In: Wu Z.-Y. & Raven P.H. (eds.), Flora of China 6: 391-431. Science Press, Miss. Bot. Gard. Press [available online at: http://flora.huh.harvard.edu/china/PDF/PDF06/RANUNCULUS.pdf]
Whittemore A.T. (1997) Ranunculus. In: Flora of North America Editorial Committee (eds.), Flora of North America, vol. 3. Oxford University Press, New York-Oxford: 88-135. [available online at: http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=127971]