In the 1800's the roots of the marshmallow plant (Althaea officinalis) were used to make a homemade confection that took its name from the plant root. Confectioners developed a mass-produced version in the early 1900's and switched to corn syrup and egg whites to achieve the consistency of the original. This is probably a truely American food, spawning marshmallow fluff, Rice Krispie treats, fruit salads and sweet potato casseroles.

Thanks to Thanksgiving 101 by Rick Rogers for this tip.