This picture is of commercially made sugarplum candy, but originally, the word "sugarplum" was another name for "comfit." Comfits are seeds or fruit that are sugar-coated. The earliest comfits were made from seeds such as anise, caraway, fennel and coriander.
Later, the word "plum" referred to all fruits. Comfits began to be made of fruits, such as oranges, lemons, gooseberries, cherries, currants and raspberries. Cinnamon, ginger, and orange rinds were cut into slivers and also made into comfits. The comfits were rolled in sugar and dried and became known as "sugarplums."
The image of commercially made Sugar Plums is from Amazon.