A video of the Skaggerak region that shows one species of the small aquatic plants collectively known as "frogbit" (which is actually several species) opening up. You can see the pistils are sometimes quite extended and there's a light fringe on the edge of the petals. These features are present in the VMS drawing and are not characteristic of the larger water lilies (or the ones with multiple petals).
See 34:30
Also, if you stop the video at 34:34 and look closely, you will see a line running up the middle of the petal. It's not apparent in this variety, but in some species, the "line" is quite distinctly triangular, which is another detail included in the VMS drawing. The calyxes on the different species differ—some are blunt, some are pointed like this one. Some have a little "shelf" similar to the VMS drawing.
I'm not insisting the drawing has to be one of the frogbits, but in terms of matching features, it scores very high.
See 34:30
Also, if you stop the video at 34:34 and look closely, you will see a line running up the middle of the petal. It's not apparent in this variety, but in some species, the "line" is quite distinctly triangular, which is another detail included in the VMS drawing. The calyxes on the different species differ—some are blunt, some are pointed like this one. Some have a little "shelf" similar to the VMS drawing.
I'm not insisting the drawing has to be one of the frogbits, but in terms of matching features, it scores very high.