Main Difference -Yams vs Sweet Potatoes
Yams and sweet potatoes are angiosperms (flowering plants) and known as one of the main staple starchy food group. They are more or less similar in their morphological and physiological features and it becomes difficult to separate those different features correctly and distinguish one from the other. However, their botanical classification is the predominant feature that can be used to differentiate them. Yams are monocots (a plant having one embryonic seed leaf) and are known as monocot plants and belong to the Dioscoreaceae family. In contrast, sweet potatoes are dicot plants or in other words, a plant having two embryonic seed leaves and belong to the Convolvulaceae family. This is the main difference between yams and sweet potatoes.
What are Yams
Yams belong to the family Dioscoreaceae and are grown in larger quantities and provide more food energy and carbohydrate for the entire world. In addition, they are considered as staple crops in many Asian and African countries. They are perennial herbaceous vines and are closely related to grasses or lilies. There are over 600 varieties of yams and almost all the varieties are cultivated in Africa. Edible yam tubers vary in size and shape. For example, tubers can grow up to 1.5 meters in length and weigh up to 70 kg. The tuberous yam vegetable has a very rough and pebbly skin which is difficult to peel, but which softens after boiling. The peel of yams varies in color from dark brown to light pink. Yams are a rich source of macronutrients and micronutrients as well as bioactive phytochemicals (polyphenols, flavonoids, anthocyanin, carotenoids etc.). However, immature yams may contain tannin and phytic acid as anti-nutritional factors and bitter toxic compounds.
What are Sweet Potatoes
Sweet potatoes (Ipomoea batatas) belong to the family Convolvulaceae also known as morning glory family and are big, starchy, sweet, tuberous root vegetables. Sometimes fresh and immature leaves and shoots are also used for consumption. They are used as food for humans as well as animals. Sweet potatoes are cultivated agriculturally, primarily for their human food grain seed, for livestock forage, silage production, and as soil-enhancing green manure. The peel color varies in color from white to yellow, red, purple or brown. The edible flesh also varies in color from white to yellow, orange, or orange-red. Some selected soft varieties of sweet potato are also known as yams in some parts of the United States and Canada.
Difference Between Yams and Sweet Potatoes
Yams and sweet potatoes may have substantially different properties and applications. These differences may include,
Plant Family and Cultivars
Yams: Yams are classified under different genera of Dioscorea/ Dioscoreaceae family. It consists of more than 600 varieties, and major cultivated species include;
- Dioscorea rotundata and D. cayenensis
Sweet potatoes: Sweet potatoes belong to the family Convolvulaceae and its botanical name is Ipomoea batatas. It consists of 50 genera and more than 1,000 species.
Categorization Based on Cotyledons
Yams: Yams are monocotyledonous plants.
Sweet potatoes: Sweet potatoes are dicotyledonous plants.
Sweet potatoes: 2n=90
Plant Origin and History
Yams: Yams are inborn to Africa and Asia.
Sweet potatoes: Sweet potatoes are inborn to tropical regions in the Americas.
Yams: Tuber, and immature leaves and shoots of some varieties are edible.
Sweet potatoes: Roots and immature leaves and shoots are edible.
Appearance of Peel
Yams: They have a rough and scaly appearance.
Sweet potatoes: They have a smooth appearance with a thin skin.
Colour of Peel
Yams: Yams often have a dark brown to light pink color.
Sweet potatoes: The peel is yellow, orange, red, brown, purple or beige color.
Shape of Tuber/Root
Yams: The shape is long, cylindrical, some have “toes”.
Sweet potatoes: The shape is short, blocky, with tapered ends.
Colour of Flesh
Yams: The color of the flesh is white, yellow, purple or pink
Sweet potatoes: The color of the flesh is white, red, pink, violet, yellow, orange or purple. White or pale yellow colored sweet potatoes are less sweet and moist than red, pink or orange flesh sweet potatoes.
Taste of Flesh
Yams: Yams have a starchy taste.
Sweet potatoes: Sweet potatoes have a sweet taste.
Taste and Mouth Feel of Flesh
Yams: Yams have a starchy taste and dry mouth feel.
Sweet potatoes: Sweet potatoes have a sweet taste and moist mouth feel.
Beta Carotene and Vitamin A Rich Source
Yams: Yams are usually very low in Beta-carotene and it is not considered as vitamin A rich source
Sweet potatoes: Sweet potatoes are usually high in Beta-carotene and it is considered as vitamin A rich source.
Yams: Yams are propagated from tuber pieces.
Sweet potatoes: Sweet potatoes are propagated from transplants/vine or shoot cuttings.
Categorization Based on Firmness
Yams: Yams are not categorized based on the firmness.
Sweet potatoes: Two types and they are,
- Firm sweet potatoes – Golden skin and paler flesh. After cooking, they still remain firm and a little waxy
- Soft sweet potatoes – Copper skin and orange flesh. After cooking, they become creamy, fluffy, and moist
Yams: Leading producers are Nigeria, Ghana, Ivory Coast, Benin, and Tongo.
Sweet potatoes: Leading producers are China, Uganda, Nigeria, Indonesia and Tanzania.
Toxicity and Health Concerns
Yams: Cassava may comprise a harmful toxin called cyanogenic glucosides, linamarin and lotaustralin and bitter yams may contain polyphenols or tannin-like anti-nutritional compounds.
Sweet potatoes: Sweet potatoes do not contain toxic compounds.
In conclusion, both yams and sweet potatoes are tuberous root vegetables that derive from a flowering plant, but they are not botanically related to each other.
Woolfe, Jennifer A. (1992). Sweet Potato: An Untapped Food Resource. Cambridge, UK: Cambridge University Press and the International Potato Center (CIP). ISBN 9780521402958.
Uwaegbute, Osho and Obatolu (1998). Postharvest technology and commodity marketing: Proceedings of a postharvest conference. International Institute of Tropical Agriculture. p. 172. ISBN 978-978-131-111-6.
Roots, Tubers, and Plantains in Food Security: In Sub-Saharan Africa, in Latin America and the Caribbean, in the Pacific. FAO. 1989. ISBN 978-92-5-102782-0.