Kimberly Jo Salyer, age 11, of Indianapolis, Ind., for her question:
ARE YAMS THE SAME AS SWEET POTATOES?
By the time they get to the dinner table, yams and sweet potatoes look and taste very much alike. In fact, if your taste buds are not alert, you may have a hard time telling which is which. Nevertheless, plant experts tell us that these two tasty vegetables are not even related to each other.
In the supermarket, sweet potatoes look somewhat like ordinary potatoes, tapered at each end and tinted with a brownish pink blush. Yams look like large and thicker sweet potatoes, tinted yellowish brown. These similar vegetables belong in three different families of the plant world.
This may seem odd, for both yams and sweet potatoes grow leafy vines and the part we eat is produced underground. However, there are telltale differences in both their leaves and roots. The sweet potato leaf is heart shaped and zigzagged with a network of veins. This proves that it is a dicot, belonging in one of two major divisions of the plant world.
The smooth leaves of the yam have veins that run side by side in neat parallel lines. This means that the plant belongs to the large group of monocots. Other differences show up in the two underground root systems. The sweet potato grows a network of pale roots that soaks up moisture from the soil. The thriving greenery upstairs produces surplus food which is changed into starchy material and stored downstairs in the bumps we call sweet potatoes.
The yam sends down a special branch of stringy roots called a tuber. It stuffs itself with food and nourishment and grows big enough to go to market. To a botanist, the yam tuber is different from the bulging root of a sweet potato. The sweet potato belongs in the same family as the lovely morning glory. The yam shares a different plant family with 50 or so yammy cousins. Ordinary potatoes belong in the same family as tomatoes and petunias.
As a rule, yams are slightly more expensive than sweet potatoes because they must be shipped from mild, moist regions. The sweet potato grows closer to home. However, where summers are short, we must start the vines indoors. This is no problem, when one end of a sweet potato is placed in a glass partly filled with water and placed on a sunny window sill. It helps to stick a few toothpicks in it to prevent the potato from touching the bottom of the glass.