Lise Ann Lieder, age 8, of Houston, Texas, for her question:
Are yams different from sweet potatoes?
Most of us tend to think that a yam is just a special sort of sweet potato. But an expert who studies plants does not agree with this idea. He is a botanist and a botanist insists that the yam and the sweet potato come from two entirely different plants. In fact, he even classes them in two plant families that are not even related to each other. Maybe so. But a helping of sweet potato looks and tastes very much like a helping of delicious yam.
In the market, sweet potatoes cost a bit less than yams because they are grown right here in the United States. In fact, you can coax one to start growing in a glass partly filled with water. Prod in three toothpicks to keep one end above water level and place it on a sunny window sill. Notice the small dents in the sweet potato's skin. These are buds called eyes. In a few days, they will sprout bunches of tiny leaves. In a few weeks, they become trailing vines of delicate greenery. Later, if you plant your thriving sweet potato in the garden, chances are it may grow several new sweet potatoes. Every year, crops of them are grown in Louisiana and North Carolina, Virginia and New Jersey.
Yams cost a little more because they prow only in certain warm tropical countries and shipping them here adds to the price. At one time, the only places to find them were in Africa. Now they have been coaxed to grow in many other warm, moist regions. Both yams and sweet potatoes grow underground and both the plants are trailing vines. You might think the two are cousins. But the botanist points out a few differences ¬and proves that they are not even related.
Ha, says the expert. Observe their leaves closely. The sweet potato vine has heart shaped leaves with pointed edges. The leaf veins zig zag around in a lacy network. This proves that this plant is a dicot. Now notice the smooth leaves on the yam vine. Their veins run neatly side by side. This proves the plant is a monocot. And to a botanist, monocots and dicots are very different plants.
Our botanist friend points out more differences underground. The sweet potato grows a network of pale roots that soak moisture and nourishment from the soil. The thriving greenery upstairs makes plant food, with some to spare. The extra food is changed into starchy material and sent downstairs to be stored in the roots. It is stored in those brownish bumps we call sweet potatoes. The yam sends down a special branch instead. of stringy roots. It is called a tuber and it too soaks up moisture and nourishment from the soil. The yams we eat are parts of the tuber that are stuffed with extra supplies of starchy food. To a botanist, a yam tuber is very different from the root of a sweet potato, though both have eyes to sprout new plants.
The ordinary potato also grows on underground roots. But the botanist classifies the yam, the sweet potato and the ordinary potato in three different plant families. The ordinary potato is a cousin of the tomato, the eggplant and the petunia. The sweet potato belongs to the same family as the blue eyed morning glory. The yam has about 20 yammy cousins and they have a plant family all to themselves.