Sweet Potatoes and Yams

Tonight for dinner I made grill cheese sandwiches and sweet potato chips. The sweetness of the sweet potato and the saltiness of the chip combined to make a great side dish. However, while eating them I began to wonder about the history of the sweet potato. Over Thanksgiving I learned that it was not a relative of a yam, which intrigued me and helped to lead to this post.

The sweet potato is a relative of the morning glory family, Convolvulacea, and has many different varieties. This plant has its beginnings in prehistoric South America and comes in a range of skin and flesh colors. Furthermore, there are two distinct groupings of sweet potato varieties, "soft" and "firm". It is the ones in the "soft" category that have caused the confusion with yams.

During the time of slavery in the south, sweet potatoes were brought from South America and used as a staple food source for slaves. Slaves seeing and cooking with the "soft" variety of sweet potatoes believed them to be nyami, an edible starchy root that is grown throughout Africa. The name was changed to yam and stuck.

However, the nyami and the sweet potato are quite different botanically speaking. For one the nyami is a monocot group, which means that they only have one seed-leaf or cotyledon. Whereas the sweet potato is a dicot or a plant that has two seed-leaves or cotyledons. The sweet potato is originally from Peru and Ecuador and the nyami is originally from West Africa and Asia. Lastly, the sweet potato has half the growing season as the nyami.

In the grocery store most of the "yams" that you will see for sale are actually a "soft" variety of sweet potato. All true yams or nyami must be grown in a warmer climate such as the carribean due to the exceptionally long growing season. So we don't actually see them for sale very often here in the United States and can only usually be found in an international market.

Today the U.S. Department of Agriculture requires labils with the term yam to be accompanied by the term sweet potato.

	Factor	Sweetpotato	Yam
1.	Scientific Name	Ipomoea batatas	Dioscorea Species
2.	Plant family	Morningglory (Convolvulaceae)	Yam (Dioscoreaceae)
3.	Plant group	Dicotyledon	Monocotyledon
4.	Chromosome number	2n=90 (hexaploid)	2n=20
5.	Flower character	Monoecious	Dioecious
6.	Origin	Tropical America (Peru, Ecuador)	West Africa, Asia
7.	Historical beginning	Prehistoric	50,000 BC
8.	Edible storage organ	Storage root	Tuber
9.	Number/plant	4 to 10	1 to 5
10.	Appearance	Smooth, with thin skin	Rough, scaly
11.	Shape	Short, blocky, tapered ends	Long, cylindrical, some with "toes"
12.	Dry matter	22 to 28%	20 to 35%
13.	Mouth feel	Moist*	Dry
14.	Taste	Sweet*	Starchy
15.	Beta carotene (Vit. A)	High (orange vars.)*	Very low
16.	Propagation	Transplants/vine cuttings	Tuber pieces
17.	Growing season	90 to 150 days (120= Jewel)	180 to 360 days
18.	Maturity	None	At senescence
19.	Storage	(Cured at 80 to 86oF) 55 to 60oF	54 to 61oF
20.	Climatic requirements	Tropical and temperate	Tropical
21.	Availability	Grown in USA	Imported from Caribbean