Aponogeton distachyos L. f. (S-Afr.) – A very rare but increasing, usually ephemeral alien. The species was introduced on purpose in a lake near Couvin (valley of river Ry de Rome; see Saintenoy-Simon & Duvigneaud 1994) and subsequently persisted for some time. Also introduced near Thozée where it was removed in 2005. In 2009 recorded for the first time in Flanders, in riverlet Wamp in Arendonk. Since 2012 recorded on several occasions in the valley of Zwart Water near Lummen, often in relative abundance. Here probably more or less naturalized in a valuable but vulnerable native habitat.
Similar records are available from neighbouring territories as well, for instance from the British Isles and France (Stace 2010, Tison & de Foucault 2014). For Dutch records, see here: http://waarneming.nl/soort/view/20440. It also naturalized locally in California in North America (Hellquist & Haynes 2000).
Aponogeton distachyos is originally native in the milder parts of South Africa and probably not fully hardy in most parts of Belgium. However, as a result of climate change it may be able to adapt to western European (continental) climate types.
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Selected literature:
Arnold A. (2016) Die Zweireihige Wasserähre (Aponogeton distachyos L. f.) im Grenzgebiet von Sachsen-Anhalt und Sachsen. Mitt. florist. Kart. Sachsen-Anhalt (Halle 2016) 21: 39–42. [available online at: http://botanischer-verein-sachsen-anhalt.de/wp-content/uploads/2017/02/F...
Hellquist C.B. & Haynes R.R. (2000) Aponogeton. In: Flora of North America Editorial Committee (eds.), Flora of North America, vol. 22. Oxford University Press, New York-Oxford: 39-40. [available online at: http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=102317]
Hussner A. (2012) Alien aquatic plant species in European countries. Weed Research 52: 297-306. [available online at: http://www.researchgate.net/publication/257650711_Alien_aquatic_plants_i...
Saintenoy-Simon J. & Duvigneaud J. (1994) A propos d’espèces introduites dans les étangs. Adoxa 3: 11-13.
Stace C. (2010) New flora of the British Isles, 3th ed.: XXXII + 1232 p. Cambridge University Press.
Tison J.-M. & de Foucault B. (coord.) 2014) Flora Gallica. Flore de France. Editions Biotope, Mèze : xx + 1196 p.