Potamogeton praelongus Wulfen (Lingua d'acqua allungata)
USDA-NRCS PLANTS Database / Britton, N.L., and A. Brown. 1913. An illustrated flora of the northern United States, Canada and the British Possessions. Vol. 1: 80.

Potamogeton praelongus Wulfen (Lingua d'acqua allungata)
Walter Hood Fitch - Illustrations of the British Flora (1924) - Permission granted to use under GFDL by Kurt Stueber. Source: www.biolib.de - Permission is granted to copy, distribute and/or modify this image under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the section entitled "GNU Free Documentation License".

Potamogeton praelongus Wulfen (Lingua d'acqua allungata)
Hippolyte Coste - Flore descriptive et illustrée de la France, de la Corse et des contrées limitrophes, 1901-1906 - This image is in public domain because its copyright has expired.