Yams and sweet potatoes are vegetables that are often mistaken for each other. In some regions, like the United States, sweet potatoes are marketed as yams. In fact, as per the U.S. Department of Agriculture rules, packs with sweet potatoes must have an additional label with the term 'yam' printed on them. All these factors add up to the confusion about the difference between sweet potatoes and yams.
Yams Vs Sweet Potatoes
Even though the terms sweet potatoes and yams are used interchangeably, both are entirely different vegetables. Some types of yams resemble sweet potatoes in appearance, and this could be a possible reason for confusion. Marketing of these vegetables using both the terms worsens the confusion. The truth is that, yams and sweet potatoes are entirely different vegetables.
Yams and sweet potatoes belong to two entirely different plant families. While yams belong to genus Dioscorea of Dioscoreaceae family, sweet potatoes (Ipomoea batatas) are classified as a member of the genus Ipomoea and family Convolvulaceae. While yams can be related to lilies and grasses, sweet potatoes can be distantly related to potatoes.
Sweet potatoes are also referred to as 'tuberous morning glory', as the family include garden flowers called morning glories. While the edible part of yams are tubers, sweet potatoes are storage roots. It is believed that yams originated in tropical regions, like Africa and Asia, whereas sweet potatoes are native to the tropical regions of America, Peru and Ecuador. There are around 600 species of yams, but only six to seven of them are cultivated as major crops.
Shape and Size
You can also distinguish between yams and sweet potatoes by checking the shape and size of the vegetable. While sweet potatoes have thin and smooth skin, yams have a thick and rough skin, which can also be scaly. Some types of yams have a bark-like skin. As far as the shape is concerned, sweet potatoes have somewhat tapered ends, and are comparatively short and stubby. Most of the yams are cylindrical and long, but some varieties have a round shape, like a big bowl. Yams can grow so big and long, that sometimes they reach a length of around seven feet and more.
Skin and Flesh Color
The difference between yams and sweet potatoes can be made out from the color of the vegetable. The skin color of yams ranges between brown to black, whereas in case of sweet potatoes, it can be pale yellow, orangish yellow, red, or purple. While the flesh of yams can be off-white, pale yellow, purple, or red; the flesh color of sweet potatoes is pale yellow in almost all varieties, except the orange one with a bright orange flesh. The flesh color of both vegetables may vary with the variety.
Taste and Texture
Yams and sweet potatoes can be differentiated through their taste and texture. While sweet potatoes are sweet (orange skinned ones being sweeter than the pale yellow one), yams are more starchy. While sweet potatoes are more moist (pale yellow one is slightly crumbly too), yams have a dry texture.
It is said that, initially only the soft and dark-skinned variety of sweet potatoes were cultivated in the United States. The African slaves used to call these vegetables yams, as they looked like real yams of Africa. So when the hard varieties with pale skin were introduced, there was a confusion. This led to the existing sweet and dark-skinned ones to be termed yams and the latter entrant as sweet potatoes. However, the confusion still continues. With the tips mentioned above, you can easily distinguish between these two vegetables.