Identificaciones de dryopteris2

Live plants collected in the field at the mapped location (bridge over Oromocto River near Sunpoke Lake, NB on August 17, 2023). Grown to maturity at Sackville NB.
@elizabeth1067 @dryopteris2 - Does this ID look correct to you? This is a rare species in our region, the identity of which has been questioned by outside experts. It grows on seasonally exposed shores of our largest river (Saint John, aka Woolastook) with S. tradescantii but looks distinctly different and appears to mature later as well. It is clearly different to my eye from any form of S. lateriflorum. We don't have other small white aster species here except for rare roadside introductions of S. pilosum, and I'm confident it isn't that species. Thanks for your opinions!

I believe this is Yellow Nutsedge (cyperus esculentus)?
There is a lot of this growing in the mud flats, that are under water in Summer. I can get more pictures if there is something else need for identification. This was one of the largest plants.
I think the photo of the base of plant distinguishes this from Cyperus odoratus.