Pondweed ID

[Tiggrx]

Does this Pondweed look familiar to anyone? There was a large metal fence between me and it, so was unable to look at a specimen closely.

It was growing in fastish flowing water in a canalized stretch of the River Ash near Staines, Surrey

[KeenTeen17]

Unfortunately these aren't my specialty. Flicking through the book, Potamogeton crispus looks like a contender

[AlanS]

Hi Tiggrx,

The photograph is a bit puzzling, but I think it is most likely Potamogeton lucens (Shining Pondweed).

The apparent floating leaves, that P. lucens does not have of course, cause some thought, but it looks from the photograph as though they are not true "floating leaves", but are just leaves that have reached the surface and so are ... er ... floating. The edges are mostly rolled up and they don't have that very flat, leathery look.
The underwater leaves look just right for P. lucens and seem to rule out most other possible candidates.

There is, of course, a hybrid of lucens with natans (P. x fluitans), but rarity and geography would appear to rule that out.

Alan

[Tiggrx]

Thanks for the responses.

Alan - I hadn't considered P. lucens because of the floating leaves, but it is a possibility. It is a species I have seen several times and am fairly familiar with, however I usually have seen it in different environmental conditions (i.e. slower moving water).

My best guess had been P. nodosus, which I was certainly out of range of.

[AlanS]

Oops. I really should learn not to post quickly late at night.

It is NOT P. lucens, for all that I have seen it looking a bit like that. Some of the leaves have long petioles and that rules out P. lucens.

I did wonder about P. nodosus and rejected it as a possibilty on geography, but .... ??

My only other suggestion now is P. natans that has been subject to a sudden rise in water level and so doesn't have the usual underwater leaves. That was my first reaction to the photograph, but I persuaded myself it wasn't. But perhaps after all ...?

Apologies for an unhelpful attempt at ID.

Alan

[AlanS]

Oh ho. I forgot that having clicked on the thumbnail to see the photo, a further click can give an enlargement.

One floating leaf is clearly of P. natans type, and towards the bottom left it is possible, I think, to make out a couple of the genuine, long, linear P. natans submerged leaves, deeper in the water below the submerged 'floating' leaves.

I am sure, now, that this is the answer.

Sorry again for previous wrong suggestion.

(Sigh. Multiple years ago I ran a weekend aquatic plants course for the old Nature Conservancy and pointed out all these traps.)

Alan

[Tiggrx]

Thanks Alan.

There was plenty of P. natans in a nearby gravelpit so it is very likely that is what it is. I don't think I have ever come across it is flowing water before.