Skip over navigation to text  The Library of Congress >> Research Centers >> Science Reference Services  
Everyday Mysteries: Fun Science Facts from the Library of Congress  
<< HOME           << See More Everyday Mysteries>>       << Ask a Question >>   
Find in

    What is the difference between sweet potatoes and yams?


    Although yams and sweet potatoes are both angiosperms (flowering plants), they are not related botanically. Yams are a monocot (a plant having one embryonic seed leaf) and from the Dioscoreaceae or Yam family. Sweet Potatoes, often called ‘yams’, are a dicot (a plant having two embryonic seed leaves) and are from the Convolvulacea or morning glory family.

Yams are closely related to lilies and grasses. Native to Africa and Asia, yams vary in size from that of a small potato to a record 130 pounds (as of 1999). There are over 600 varieties of yams and 95% of these crops are grown in Africa. Compared to sweet potatoes, yams are starchier and drier.

Sweet Potatoes
The many varieties of sweet potatoes (Ipomoea batatas) are members of the morning glory family, Convolvulacea. The skin color can range from white to yellow, red, purple or brown. The flesh also ranges in color from white to yellow, orange, or orange-red. Sweet potato varieties are classified as either ‘firm’ or ‘soft’. When cooked, those in the ‘firm’ category remain firm, while ‘soft’ varieties become soft and moist. It is the ‘soft’ varieties that are often labeled as yams in the United States.

Why the confusion?
In the United States, firm varieties of sweet potatoes were produced before soft varieties. When soft varieties were first grown commercially, there was a need to differentiate between the two. African slaves had already been calling the ‘soft’ sweet potatoes ‘yams’ because they resembled the yams in Africa. Thus, ‘soft’ sweet potatoes were referred to as ‘yams’ to distinguish them from the ‘firm’ varieties.

Today the U.S. Department of Agriculture requires labels with the term ‘yam’ to be accompanied by the term ‘sweet potato.’ Unless you specifically search for yams, which are usually found in an international market, you are probably eating sweet potatoes!

Standard DisclaimerRelated Web Sites

Library of Congress Web SiteFurther Reading
  • Coursey, D. G. Yams: an account of the nature, origins, cultivation and utilization of the useful members of the Dioscoreaceae. London, Longmans, c1967. 230 p.
  • Davidson, Alan. Sweet potato. In The Oxford companion to food. New York, Oxford University Press, c1999. p. 774-775.
  • Davidson, Alan. Yam. In The Oxford companion to food. New York, Oxford University Press, c1999. p. 856-857.
  • Edmond, J. B. Sweet potatoes: production, processing, marketing. Westport, CT, AVI Publishing Company, c1971. 334 p.
  • Kiple, Kenneth F., and Kriemhild C. Ornelas, eds. Sweet potatoes and yams. In The Cambridge world history of food. New York, Cambridge University Press, c2000. p. 207-218.
  • Price, Robert Henderson.  Sweet potato culture for profit.  A full account of the origin, history and botanical characteristics of sweet potato.  Dallas, TX, Texas farm and ranch publishing co. 1896.  107 p.
  • Sweet potatoes and yams. New York, Medina, Ohio, The Barrett company, Agricultural dept., 1918.  15p.
  • Sweet potatoes getting to the root of the demand. Agricultural outlook, no. 269, Nov. 2002: p. 13-16.
  • Voorhees, Don. What’s the difference between a sweet potato and a yam? In Why does popcorn pop? Seacaucus, NJ., Carol Pub. Group, c1995. p. 42-43.

SearchFor more print resources...
Search on "Cooking (Sweet potatoes,)," "Sweet potatoes," or "Yams" in the Library of Congress Online Catalog.

New sweet potato cultivar Ruddy
Agricultural Research Service,
U.S. Department of Agriculture.

Man coming out of jungle with wild yam "cabezo de negro". Prints & Photographs Division, Library of Congress.

A watercolor sketch, ca. 1930, by Ibo artist D. L. K. Nnachy, depicts a dance celebrating the harvest of new yams. ( Reproduced by courtesy of the Harmon Foundation)

Drawing: two sweet potatoes with a vine in the background.
Sweet potato or yam with plant growing in the background. Prints & Photographs Division, Library of Congress.

Picking up and loading sweet potatoes. Prints & Photographs Division,
Library of Congress.

Preparing sweet potatoes for dinner.
Prints & Photographs Division,
Library of Congress.

Top of page

Top of Page

<< HOME           << See More Everyday Mysteries>>       << Ask a Question >>
 The Library of Congress >> Researchers >> Science Reference Services
 April 5, 2017
Legal | External Link Disclaimer
Contact Us