Several decades ago, when orange-fleshed sweet potatoes were introduced in the southern United States, producers and shippers desired to distinguish them from the more traditional, white-fleshed types. The African word nyami, referring to the starchy, edible root of the Dioscorea genus of plants, was adopted in its English form, yam. Yams in the United States are actually sweetpotatoes with relatively moist texture and orange flesh. Although the terms are generally used interchangeably, the U.S. Department of Agriculture requires that the label "yam" always be accompanied by "sweetpotato." The following information outlines several differences between sweetpotatoes and yams.
| Factor | Sweetpotato | Yam |
|---|---|---|
| Scientific name | Ipomoea batatas | Dioscorea Species |
| Plant family | Morningglory (Convolvulaceae) | Yam (Dioscoreaceae) |
| Plant group | Dicotyledon | Monocotyledon |
| Chromosome number | 2n=90 (hexaploid) | 2n=20 |
| Flower character | Monoecious | Dioecious |
| Origin | Tropical America (Peru, Ecuador) | West Africa, Asia |
| Historical beginning | Prehistoric | 50,000 BC |
| Edible storage organ | Storage root | Tuber |
| Number/plant | 4 to 10 | 1 to 5 |
| Appearance | Smooth, with thin skin | Rough, scaly |
| Shape | Short, blocky, tapered ends | Long, cylindrical, some with "toes" |
| Dry matter | 22 to 28% | 20 to 35% |
| Mouth feel | Moist* | Dry |
| Taste | Sweet* | Starchy |
| Beta carotene (Vitamin A) | High (orange vars.)* | Very low |
| Propagation | Transplants / vine cuttings | Tuber pieces |
| Growing season | 90 to 150 days (120 = Jewel) | 180 to 360 days |
| Maturity | None | At senescence |
| Storage | (Cured at 80 to 86°F) 55 to 60°F | 54 to 61°F |
| Climatic requirements | Tropical and temperate | Tropical |
| Availability | Grown in USA | Imported from Caribbean |
* Characteristic of most sweetpotato varieties grown in the United States
Publication date: Jan. 30, 1998
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