I think those actually are marshmallows, the way they grow, before they are cut into the bite-size pieces seen neatly packed in stores. They are a type of fungus, similar to mushrooms. Like mushrooms, those are just the fruiting bodies you see above ground, as opposed to the mycelium underground. They’ve been bred by marshmallow farmers for several centuries to become that large; feral ones are much smaller.
In the farmland area where I once lived (See this post), farmers made bales that size and shape but didn’t wrap them in anything. One farmhouse about a mile down the road had one in front of his house with two legs sticking out the end of it.