Leonurus cardiaca L. (Eur., W-As.) – Two subspecies can be distinguished in Belgium (subsp. cardiaca as an archaeophyte and subsp. villosus as a neophyte):
1 Stem hairy on the angles only (or occasionally with some hairs on the sides as well); hairs very short and appressed (often more or less curled), up to 0,5 mm long === subsp. cardiaca
Stem hairy all around; hairs patent, 1-2 mm long === subsp. villosus
Subsp. villosus (Dum.-d’Urv.) Hyl. (syn.: L. villosus Dum.-d’Urv., L. canescens Dum., L. quinquelobatus (Gilib.) Gilib. nom.inval.?, L. cardiaca var. villosus (Dum.-d’Urv.) Benth.) (E-Eur., As.) – A rare but poorly known alien. Already known to Dumortier (1827; as L. canescens) from Tournai (“in ruderatis”) and subsequently confirmed from several places by Durand (1899). However, completely neglected in Belgium in the past decades (see for instance Lambinon & al. 2004). A herbarium revision yielded several records from widely scattered localities (Verloove 2006), older as well as more recent ones. Collected for instance in a wood margin in Baudour in 1892 and near a castle in Waasmunster (Roodebosh-Uilenkasteel) in 1903. Subsp. villosus was well-established at the ruins of a church in Genk, at least between 1911 and 1948. Furthermore recorded from Falaën in 1925 (foot of wall at the Boel estate). Finally, in the past decades seen in Ogy in 1979 (waste land), Orval in 1985 (roadverge), Gits in 1987 (railway station), Woluwe-Saint-Pierre in 1991 (ground heap) and Lommel (2011-2012).
Subsp. villosus is much rarer than subsp. cardiaca but possibly overlooked. In parts of western Germany – close to the Belgian frontiers – it is now commoner than subsp. cardiaca (Dickoré & al. 2009, Reichert & Fritsch 2009). It is cultivated by bee keepers and apparently also often introduced for “wild gardening”. Its degree of naturalization in Belgium is unknown. It should be looked for in the surroundings of the localities where it was found in the past decades.
Both subspecies are well-separated in Belgium. However, in areas where both more frequently grow together intermediate plants are sometimes found. These might as well represent locally arosen (sterile?) hybrids or more or less stable hybridogenous (fertile) species. The latter have been referred to as Leonurus intermedius Holub (Holub 1993). Recent molecular data, however, have demonstrated that subsp. villosus is better given species status (as L. quinquelobatus) and that L. intermedius is most likely a synonym of the latter (Marciniuk & al. 2014).
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Selected literature:
Ardenghi N.M.G. (2013) Leonurus quinquelobatus Gilib., esotica nuova per l'Italia (Dicotyledones Lamiaceae). Quaderno di Studi e Notizie di Storia Naturale della Romagna 37: 35-45.
Ardenghi N.M.G. (2015) Lectotypification of Leonurus quinquelobatus (Lamiaceae). Taxon 64(1): 160-162.
Dickoré W.B., Lewejohann K. & Urner R. (2012) Neufunde, Bestätigungen und Verluste in der Flora von Göttingen (Süd-Niedersachsen). Florist. Rundbriefe 42: 5-59.
Dumortier B.C. (1827) Florula Belgica. Tornaci Nerviorum, J. Casterman: 172 p.
Durand T. (1899) Phanérogames. In: De Wildeman E. & Durand T., Prodrome de la flore belge. A. Castaigne Editeur, Bruxelles: 1112 p.
Holub J. (1993) Leonurus intermedius, species nova – with additional notes on some other Leonurus taxa. Preslia 65: 97-115.
Lambinon J., Delvosalle L., Duvigneaud J. (avec coll. Geerinck D., Lebeau J., Schumacker R. & Vannerom H.) (2004) Nouvelle Flore de la Belgique, du Grand-Duché de Luxembourg, du Nord de la France et des Régions voisines (Ptéridophytes et Spermatophytes). Cinquième édition. Jardin botanique national de Belgique, Meise: CXXX + 1167 p.
Loos G.H. (1995) Bestimmungsschlüssel für die Leonurus cardiaca-Gruppe in Deutschland. Flor. Rundbr. 29(1): 30-33.
Ludwig W. (1987) Über die “Dorfpflanze” Leonurus cardiaca L. s.lat. (Lamiaceae) und ihr Vorkommen in Hessen. Jber. Wetterau. Ges. Naturk. 138-139: 17-29.
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]
Reichert H. & Fritsch R. (2009) Dritte Nachträge zur “Flora des Nahegebietes und Rheinhessens” von Alfred Blaufuss & Hans Reichert (1992). Mitt. Pollichia 94: 99-137.
Verloove F. (2006) Catalogue of neophytes in Belgium (1800-2005). Scripta Botanica Belgica 39: 89 p.