Lindernia dubia (L.) Pennell (syn.: L. gratioloides Lloyd, Ilysanthes dubia (L.) Barnh., I. attenuata (Spreng.) Small) (N-Am.) – A very rare but increasing, locally naturalized alien. Known since 1993 from several ponds in Vijvergebied Midden-Limburg near Zonhoven (Vannerom 1994, Berten 1997, Verloove 2002, Van Landuyt 2006). Lindernia dubia grows on the muddy bottom of exposed (artificial) fish ponds but also on pond margins in nature reserves (for instance Platweiers). It usually occurs in extreme abundance and a future dispersal to other suitable habitats in this area is very likely. Since 2008 it has been recorded on the gravelly banks of river Maas, at first on the Dutch part but since 2011 also in Belgium (Maaswinkel, Maesbempder Greend and in Bichterweerd even in abundance). In 2012 discovered for the first time outside of the province of Limburg (exposed pond margins in Jutse Plassen in Koningshooikt, near Lier) and in 2015 also in similar conditions in Retie (Prinsenpark; comm. D. De Beer).
Lindernia dubia usually grows along with vulnerable native species like Cyperus fuscus, Elatine div. spec., Eleocharis div. spec.,… It proliferates in natural habitats and should be regarded as an invasive species. However, its impact on native vegetation requires further study. In Koningshooikt it occurs in extreme abundance and doubtlessly out-competes native species (comm. D. De Beer). In the Netherlands, where L. dubia is a more recent alien, it is considered an invasive species that is fast spreading (Simons & Jansen 2018).
Lindernia dubia was originally introduced through pisciculture, apparently from France (along with Crypsis schoenoides and others). Similar records are available from Germany (see also von Drachenfels & al. 2004 for records of Cyperus michelianus (L.) Link).
Lindernia dubia is a rather variable species. Especially in France two more or less distinct subspecies are usually distinguished: subsp. dubia with a broadened leaf base and subsp. majus (Pursh) Pennell with an attenuate leaf base. These taxa are no longer upheld by Lewis (2000) and their taxonomic value is, indeed, questionable. Nonetheless, the Belgian populations seem to pertain to subsp. dubia (Verloove 2002).
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Selected literature
Berten B. (1997) Belangrijke vondsten van hogere planten in de periode 1994-1996 in Limburg. Dumortiera 68: 29-31.
Drachenfels O. von, Garve E., Gerker R. & Täuber T. (2004) Unerwartet neu: Cyperus michelianus (L.) Link in Niedersachsen. Flor. Rundbr. 38: 7-13.
Drobnik J. & Buchalik M. (2004) Lindernia dubia (Scrophulariaceae): nowy gatunek we florze Polski. Fragm. Flor. Geobot. Polon. 11: 5-14.
Kallen H.W. (1994) Das Grosse Buchsenkraut Lindernia dubia (L.) Pennell im Elbtal zwischen Lauenburg und Wittenberge. Flor. Rundbr. 27(2): 107-109.
Kurka R. (1990) Lindernia dubia: novy zavleceny druh v Ceskoslovensku. Zpravy Cesk. Bot. Spol. CSAV 25(2): 47-48.
Lewis D.Q. (2000) A revision of the New World species of Lindernia (Scrophulariaceae). Castanea 65(2): 93-122.
Scheuerer M. (2006) Lindernia dubia erstmals an der bayerischen Donau. Hoppea 67: 357-362.
Scheuerer M. (2007) Lindernia dubia jetzt auch im Regen-Tal bei Cham. Hoppea 68: 341.
Simons E.L.A.N. & Jansen M.G.M. (2018) Ecology of naturalized invasive species Lindernia dubia (L.) Pennell in the Netherlands. Gorteria 40: 1-10. [available online at: http://natuurtijdschriften.nl/download?type=document&docid=643565]
Sluschny H. (1999) Das Große Büchsenkraut Lindernia dubia (L.) Pennell neu für Mecklenburg-Vorpommern. Bot. Rundbr. Mecklenburg-Vorpommern 33: 41-46.
Šumberová K., Lososová Z., Ducháček M., Horáková V. & Fabšičová M. (2012) Distribution, habitat ecology, soil seed bank and seed dispersal of threatened Lindernia procumbens and alien Lindernia dubia (Antirrhinaceae) in the Czech Republic. Phyton (Horn, Austria) 52(1): 39-72.
Van Landuyt W. (2006) Lindernia dubia. In: Van Landuyt W., Hoste I., Vanhecke L., Van den Bremt P., Vercruysse W. & De Beer D., Atlas van de flora van Vlaanderen en het Brussels gewest. Instituut voor Natuur- en Bosonderzoek, Nationale Plantentuin van België en Flo.Wer: 545.
Vannerom H. (1994) Omtrent de vondst van Lindernia dubia (L.) Pennell (Scrophulariaceae), nieuw voor de Belgische Flora, en de evolutie van de Platweiers te Zonhoven (prov. Limburg). Dumortiera 55-57: 23-26.
Verloove F. (2002) Ingeburgerde plantensoorten in Vlaanderen. Mededeling van het Instituut voor Natuurbehoud n° 20: 227 p.