Marsh plant of St.Lawrence River

This plant was collected in a coastal marsh of St.Lawrence River in the end of June 2007. I was not able to identify it. Maybe someone can help? Sorry for the bad shape of the plant - it has very soft tissues and was photographed next day.

 

Were the lower leaves submerged? And it seems like the leaves emerge opposite?

 

It was collected in a Typha angustifolia marsh that is flooded only in spring but has water table almost at surface in June. The plant is very delicate and dries out quickly, leaves definitely opposite.
Here is the list of other species at the site with percent cover:
Typha angustifolia 85
Impatiens capensis 20
Calamagrostis canadensis 5
Polygonum amphibium 2
Onoclea sensibilis 0.5
Lysimachia thyrsiflora 0.3
Lythrum salicaria 0.1
Lycopus eurapeus 0.1
Scutellaria galericulata 0.1
Galium trifidum 0.1
Cicuta bulbifera 0.1
Galium trifidum 0.1
Solanum dulcamara 0.1
Polygonum sagittatum 0.1
Mentha arvensis 0.1
Equisetum fluviatile 0.01

 

The fruit bears an amazing resemblance to an ink pen.

 

Then it must be a maple!

 

Yup, sugar maple.

Sepo, you may have answered your own question. Have you checked each of the species on your list against your sample plant? Should be easier for you since you know what it looked like before it shrivelled up like that.

I'd say your most likely suspect is the Cicuta.

 

Not Cicuta, that (like all Apiaceae) has alternate leaves, not opposite like the mystery plant.

Off topic, but the Canadian flag's maple leaf isn't Sugar Maple, it was deliberately drawn to be a generic maple leaf, not one species in particular, so that it wouldn't be biased in favour of any one province.

 

You know, I should have known that.

And if you blow up photo #1 you can see that those aren't opposite leaves, they've just dried in that position - there's only a budnode on one side of the stem. Or at least that's how it looks to me.

 

sepo is pretty definite about them being opposite.

So... not Lamiaceae (stems are terete)

Possibly a Veronica, but I can't find any that have matching foliage with that habitat (it also looks a bit too large for most of the marshy Veronica that I've encountered)

Doesn't really have the look of a Caryophyllaceae...

 

Looks like some monocot to me.

Consider a species that is normally submerged, like a Potamogeton.

 

Thanks to everyone for this vivid discussion. I followed a hint that it might be a Scrophuliacea and seached for something similar.
One candidate is Leucospora multifida, it has similar leaves and fits by habitat and range.
Please see the picture below. The problem is that L.m. is villosulous and my specimen is not. May be it grew in shage...
From Veronica only European V.dillenii has similar leaves but it grows in drier habitats.
I also looked among monocots and couldn't find anything similar.
It is certainly not one of the species list for the site. I wouldn't post it if I knew it.