The Solanaceae Family

The Solanaceae family is more commonly known as the Potato or Deadly Nightshade family. The reason our most useful vegetable and one of the most poisonous plants are in the same family is because they share similar characteristics, both contain chemical compounds called alkaloids. There are, of course, other reasons for them to be in the same family and physical structures such as flower shape, petal arrangement, leaf shape and arrangement and other morphological structures which I won’t go into because I’m sure most of you aren’t interested in things like ‘placentation type’ and if you are then you already know about it anyway.

Although potatoes and deadly nightshade both have alkaloids and many alkaloids are highly poisonous, all the Solanaceae don’t necessarily have the same alkaloids. Atropa belladonna (deadly nightshade) is poisonous because of the alkaloid atropine which is a tropane alkaloid and although it is highly poisonous it is also a very useful drug. Many species in the solanaceae family have atropine and other tropane alkaloids in their stems and leaves including the ones that we cultivate for food.

Potato has the glycoalkaloid solanine which many people think is the green colour tubers go when exposed to light but this is not correct. Solanine is colourless but forms when tubers are exposed to the light and the green is because of chlorophyll being produced in reaction to light. There is no relationship between the amount of green on the tuber and the amount of solanine formed, so you can’t tell how much solanine might be in your green potatoes from looking at them. The green tomato-like berries that potatoes produce and their leaves and stems also contain solanine.

Potatoes are a very unusual plant; the tubers that we eat are actually swollen stems called stolons. As they grow stolons will either grow into stems with leaves on or they will grow tubers. The reason we earth up potatoes as they grow is to make the plant produce more tubers, by covering the stolons in soil we make them produce tubers by blocking out the light. Some people now use black plastic or straw to mulch their potatoes and this works in the same way though with the black plastic only stolons which happen to grow under the plastic will produce tubers.

The tomato also has a similar glycoalkaloid in its leaves, stems and green fruit called tomatine which is also toxic but only present in small amounts so it is possible to use green tomatoes when they have been cooked. Tomatine is not present in ripe tomatoes.

The solanaceae family has a lot of valuable food plants others include peppers, chillies, egg plant, gojiberry, cape gooseberry/physalis, huckleberries which look just like large deadly nightshade plants; and my personal favourite which most of you won’t have eaten the Tamarillo/tree tomato. Many popular national cuisines would be lost without this plant family. Others are grown for their appearance one of the most popular summer garden flowers the Petunia is in this family along with Brugmansiaand Nicotiana one species of which is also grown in vast quantities for another alkaloid Nicotine to which large numbers of people are addicted.

Jude Ongeri