Ballota nigra L. subsp. nigra (syn.: B. ruderalis Swartz, B. nigra subsp. ruderalis (Swartz) Briq.) (N and E-Eur.) – A rare but probably overlooked, locally naturalized alien. Collected as wool alien in 1907 in Bouvegnez in the valley of river Vesdre. Soon afterwards also seen in Wandre (1908), Lambermont (1913) and Jalhay (1913) (the latter record near a mill and possibly associated with cereals). Lawalrée (1959) further cites records from Antwerpen (1889), Lontras-Fraipont (1893), entre Vilvoorde et Haren (1920) and Braine-le-Comte (1956). Since at least 1999 known from several localities alongside the Albertkanaal between Antwerpen and Schoten (Verloove 2002), all in the surroundings of former grain mills. Here obviously well-naturalized but a future enlargement of the canal will probably destroy these populations. In 2013 also discovered in Leopoldsburg. Probably overlooked elsewhere. Also recorded in the Netherlands (Kruseman 1959, Holverda & al. 2009). Dutch records were also mostly associated with imported cereals.
Ballota nigra is a very variable species and several infraspecific taxa have been distinguished (see Patzak 1972, Sell & Murrell 2009). The distinction of both subspecies in Belgium is usually straightforward but collections with more or less intermediate features are sometimes seen. Both are best separated as follows:
1 Calyx teeth longer than broad, 3-6,5 mm long, triangular to subulate-lanceolate and gradually tapered at apex, with a distinct awn 1,5-3 mm long === subsp. nigra
Calyx teeth broader than long, 1,5-3 mm long, ovate to triangular ovate, abruptly acuminate at apex, mucronate with a mucro 0,2-1,7 mm long === subsp. meridionalis
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Selected literature:
Crespo S. (1962) Ballota nigra una Labiada nueva para la flora Argentina. Darwiniana 3: 523-527.
Holverda W., van Moorsel R. & Duistermaat L. (2009) Nieuwe vondsten van zeldzame planten in 2005, 2006 en ten dele 2007. Gorteria 34: 1-40.
Kruseman G. (1959) Ballota nigra L. aux Pays-Bas. Acta Bot. Neerl. 8: 269-270.
Lawalrée A. (1959) Révision des Ballota de Belgique de l’herbier du Jardin Botanique de l’Etat. Bull. Jard. Bot. Etat 29(4): 307-311. [available online at: http://www.jstor.org/discover/10.2307/3667128?uid=3737592&uid=2129&uid=2&uid=70&uid=4&sid=21104191499473]
Patzak A. (1972) Ballota. In: Tutin T.G. & al. (eds.), Flora Europaea, vol. 3. Cambridge University Press, Cambridge: 149-151.
Seybold S. (1972) Über die Verbreitung von Ballota nigra und Ballota alba in Württemberg. Gött. Flor. Rundbr. 6(1): 3-7. [available online at: http://species-id.net/o/media/a/a5/Flor.Rundbr._6%2C3-7_Seybold_1972_Ballota_nigra%2C_alba.pdf]
Verloove F. (2002) Ingeburgerde plantensoorten in Vlaanderen. Mededeling van het Instituut voor Natuurbehoud n° 20: 227 p.