Pontederia cordata L. (incl. P. lanceolata Nutt., P. angustifolia Pursh) (Am.) – A rather rare garden escape, throw-out or relic of cultivation. Locally naturalized and dramatically increasing in recent times. Apparently first found in 1985 in a pond near Huldenberg (Meerts 1988). Subsequently recorded in several locations but perhaps often ephemeral, except in the valley of river Nete where Pontederia cordata might have been able to naturalize recently. In 2010 also discovered, along with Vallisneria spiralis, in Ottignies (Bois de Lauzelle). Since then recorded in rather numerous and widely scattered localities. An up-to-date overview of Belgian localities is provided here: http://waarnemingen.be/soort/view/7228.
Pontederia cordata quickly builds massive stands and partly occurs in natural, vulnerable habitats in Belgium. It may be considered a potentially invasive weed and should be controlled locally. It is a declared noxious weed in many warm-temperate regions worldwide, for instance in South Africa (Henderson 2001). Even in its native American area it is considered a prolific grower and can readily cover large areas. In the British Isles it is believed to be an invasive plant causing problems (http://www.plantlife.org.uk/campaigns/invasive_plants/invasive_plants_causing_problems_in_the_uk-1/).
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Selected literature:
Clement E.J. (1980) Adventive news 18. Mixed bag. BSBI News 26: 12-18. [available online at: http://archive.bsbi.org.uk/BSBINews26.pdf]
Duvigneaud J. & Saintenoy-Simon J. (1998) Pontederia cordata L. dans le département des Ardennes (France). Adoxa 18: 3-5.
Green P. (2000) Pontederia cordata and Sagittaria rigida new to Ireland. BSBI News 83: 44. [available online at: http://archive.bsbi.org.uk/BSBINews83.pdf]
Henderson L. (2001). Alien weeds and invasive plants. A complete guide to declared weeds and invaders in South Africa. Plant Protection Research Institute Handbook No. 12: 300 pp.
Hussner A. (2007) Über Hygrophila polysperma (Roxb.) T. Anderson und Pontederia cordata L. in Nordrhein-Westfalen. Floristische Rundbriefe 40: 25-30.
Meerts P. (1988) Une famille nouvelle pour la flore adventice de la Belgique: les Pontederiaceae. Dumortiera 41: 1-3.
Scannel M.J.P. (2000) Pontederia cordata in Cork. BSBI News 84: 42. [available online at: http://archive.bsbi.org.uk/BSBINews84.pdf]
Vahle H.C. (1979) Pontederia cordata im Naturschutzgebiet Schwarze Kuhle. Kieler Not. Pflanzenk. Schleswig-Holstein 11(1): 11-12.