This is about a tuber that is especially popular on dining tables during holiday seasons. Have you ever asked yourself how marshmallows arrived atop a sweet potato casserole? It is a real shocker for non-Americans who have never seen one. In their eyes it is candy on top of a potato, and of course, that’s totally correct. Here is the story.

Let’s start with the gooey treat now called marshmallow whose name comes from the plant mallow which grows in marshy areas. Beginning as early as 2000 BC in one form or another, the plant has been used to heal wounds, soothe sore throats, toothaches, beestings, and as centuries passed its medicinal properties were used for more serious problems. But it was the ancient Egyptians who made the first sweet treat from the plant, a mixture of the plant’s sap, nuts and honey. The mixture bears no resemblance to today’s marshmallows. For centuries afterwards the plant served as a food source only in times of famine. In contrast to the sweet candy marshm...