Marshmallows get their name from a plant that is native to Europe and western Asia. The marsh mallow plant (Althea officinalis) is found growing in salt marshes and along the banks of large rivers, hence the name, "marsh" mallow.
Marshmallows date back to Egyptian times when sap from the marsh mallow root was mixed with honey and nuts to form a sweet confection which was reserved for gods and royalty. Some ancient recipes used the soft spongy pith found in the marsh mallow stem rather than the sap. The pith was boiled in a sugary syrup and then dried to create a soft, chewy candy. These candies were only available to the wealthy. Many parts of the marsh mallow plant were used for medicinal purposes. The marshmallow/honey candies were used to soothe sore throats, an ancient cough drop, as it were.
Later, the French produced a marshmallow candy that more closely resembles the marshmallows we know today. Egg white meringue was mixed with mallow root, corn syrup, and rose water, then heated and whipped to create a fluffy, sweet confection. With the advancement of production equipment and methods, marshmallows began to be mass produced and became more available to the general population.
Modern day marshmallows no longer contain any part of the marsh mallow plant. Today, gelatin has replaced the sap from the mallow root and egg whites are rarely used. Today's marshmallows are made with sugar, corn syrup, gelatin, corn starch, and flavorings.
Today, the marshmallow plant is used to treat mouth and throat ulcers and the mucilage from the roots and stems is used in cosmetic treatments and to soften skin. The edible flowers and young leaves of the plant are often used in salads.
Sources: madehow.com Wikipedia The Nibble Wikipedia