Leonurus L.
Leonurus is a genus of ca. 20 Eurasian species (much less if a broad species concept is applied). As currently accepted Chaiturus Willd. (with the European C. marrubiastrum (L.) Ehrh. ex Spenn.; syn.: Leonurus marrubiastrum L.) is excluded from it (Mabberley 2008). Molecular data also suggest a narrow generic concept (Scheen & al. 2010). One species, Leonurus cardiaca, is accepted as native in Belgium but it is at most an archaeophyte. It is fairly variable and sometimes treated as a complex of several closely related species, the Leonurus cardiacus complex (Holub 1993, Loos 1995). The extremes of this group (Leonurus cardiacus and L. villosus) are very distinct but their taxonomic value is contested. They are here accepted as subspecies but species rank may be warranted, as recently suggested by molecular data (Marciniuk & al. 2014).
Leonurus cardiaca was formerly frequently planted as a medicinal plant (less so as a bee-plant or as an ornamental). Few other species are also cultivated as ornamentals (see Whiteley 2000).
1 Calyx distinctly bilabiate, the two lower teeth patent to recurved at maturity. Cauline leaves usually shallowly 5-lobed, lobes wide === Leonurus cardiaca
Calyx not or indistinctly bilabiate, the two lower teeth straight or nearly so at maturity. Cauline leaves usually deeply 3-lobed, lobes narrow === L. japonicus
Literature:
Holub J. (1993) Leonurus intermedius, species nova – with additional notes on some other Leonurus taxa. Preslia 65: 97-115.
Jäger E.J. & Werner K. (eds.) (2005) Rothmaler Band 4. Exkursionsflora von Deutschland. Gefässpflanzen: Kritischer Band. Springer Verlag, Berlin: 880 p.
Krestovskaja T. (1992) Systematics and phytogeography of Leonurus L. Advances in Labiate Science: 139-148.
Kupryanova L.A. (1977) Leonurus. In: Shishkin B.K. (ed.), Flora of the U.S.S.R., vol. XXI. Academic Scienc. U.S.S.R.: 105-114.
Loos G.H. (1995) Bestimmungsschlüssel für die Leonurus cardiaca-Gruppe in Deutschland. Flor. Rundbr. 29(1): 30-33.
Mabberley D.J. (2008) Mabberley’s plant-book (3th ed.). Cambridge University Press, Cambridge: XVIII + 1021 p.
Marciniuk P., Gawrońska B., Marciniuk J. & Joachimiak A.J. (2014) Taxonomic individuality of Leonurus cardiaca and Leonurus quinquelobatus in view of morphological and molecular studies. Plant Syst. Evol. 300: 255-261. [available online at: http://www.readcube.com/articles/10.1007/s00606-013-0878-7]
Scheen A.-C., Bendiksby M., Ryding O., Mathiesen C., Albert V.A. & Lindqvist C. (2010) Molecular Phylogenetics, Character Evolution, and Suprageneric Classification of Lamioideae (Lamiaceae). Annals of the Missouri Botanical Garden 97(2): 191-217. [available online at: http://www.botanicus.org/item/31753003743058]
Shu Y.M.C. (1994) Leonurus. In: Wu Z.Y. & Raven P.H. (eds.), Flora of China, vol. 17. Science Press, Beijing & Missouri Botanical Garden Press, St. Louis: 162-165. [available online at: http://flora.huh.harvard.edu/china/PDF/PDF17/leonurus.pdf]
Whiteley A.C. (2000) Leonurus. In: Cullen J. & al. (eds.), The European Garden Flora, vol. 6. Cambridge University Press, Cambridge: 204.