Sagittaria latifolia Willd. (N & C-Am.) – Increasingly grown as an ornamental and recently escaping (perhaps mainly as a garden throw-out). Locally becoming naturalised in ditches or ponds. Possibly first recorded in an artificial pond in Corphalie (Amay) in 1997 (deliberately introduced but apparently well established and extending). Currently known since at least 2004 from ditches between Izegem and Lendelede (massive population over several kilometers) and in Drongen (small population). In the past years obviously increasing: additional recent records are available for instance from Diepenbeek (Pomperikvijvers, at least since 2009), Mol and Oelegem (see waarnemingen.be).
The plant usually cultivated appears to be var. obtusa (Muhlenb.) Wiegand with characteristic (mature!) leaves that much differ from those of native Sagittaria sagittifolia (see key). Leaf characters are usually not considered in European standard floras to distinguish between Sagittaria latifolia and S. sagittifolia. As a matter of fact they serve as a good feature for their distinction (as illustrated by van Ooststroom & Reichgelt 1956 and Walter 1993). However, some Belgian populations (for instance in the surroundings of Westerlo; see photo below) are aberrant and possess leaves with a long acuminate leaf apex that much ressemble those of S. sagittifolia.
Sagittaria latifolia
Sagittaria sagittifolia
Selected literature
Salanon R. (2000) Trois xénophytes envahissantes des cours d'eau, récemment observées dans les Alpes-Maritimes (France): Myriophyllum aquaticum (Velloso) Verdcourt, Ludwigia grandiflora (Michaux) Greuter et Murdet et Sagittaria latifolia Willd. Biocosme Mésogéen 16(3): 125-145.
Van Ooststroom S.J. & Reichgelt Th.J. (1956) Floristische notities 1-18. Acta Botanica Neerlandica 5: 102-114.
Walter E. (1993) Pflanzen von denen in der mitteleuropäischen Literatur selten oder gar keine Abbildungen zu finden sind. Folge XX: das Breitblättrige Pfeilkraut (Sagittaria latifolia Willd.) – neu für Oberfranken. Flor. Rundbr. 27: 55-58.