Are there reeds or reedlike wetland/marsh/swamp plants that look like marshmallows? It’s difficult to search, because apparently marshmallows are a real plant, but they are just white flowers that don’t look like the confection. The closest thing I can find so far is cattails, but they are more like corn dogs on a stick than marshmallow on a stick. I’ll also settle for any kind of online visual field guide.
Is there a specific reason that you think there would be?
I believe it’s not the fruit of the marshmallow, but the pith inside the reeds which is sweet and edible and in turn gave its name to the confection.
I’m wondering if you’re seeing cottongrass/cottonsedge, which has white fluffy seedheads.
It would be helpful if the OP would provide more detail on what he is seeing. The description is very vague. What do the “marshmallows” look like exactly?
There are cattails with shorter seed pods. Something like this, perhaps?
Edit: Here’s a picture with more variation: Dwarf Cattail reeds in pond, Typha Minima | IBuyPhotos
Small reedmace look a bit like marshmallows that have been badly toasted.
https://www.lincspplants.co.uk/media/catalog/product/cache/1/image/9df78eab33525d08d6e5fb8d27136e95/t/y/typha_minima_1.jpg
Bog Cotton
In particular, when it looks like this: Eriophorum angustifolium - Wikipedia
But that’s exactly how I like my marshmallows.
Same plant as in post #5. It has a lot of common names.