From Seed to Seed:
Plant Science for K-8 Educators

Leaves and stems. All sorts of leaves and stems are used as food by various cultures, including such unusual offerings as young fern fronds (fiddleheads) and "weeds" such as dandelion and lamb's quarters.

In general, leaves and stems provide relatively little energy value, or calories, compared to other plant parts. However, they do contain many vitamins, minerals, and trace materials that are essential to a healthful diet.

Leaves we use as food include chard, spinach, collard, kale, lettuce, and cabbage. We also eat the leaves of many herbs, such as parsley, thyme, rosemary, and sage.

We eat the stems (shoots) of asparagus and the leaf petioles of rhubarb and celery.

Recall that potatoes are modified stems. The white, or Irish, potato is one of the world's most important foods. Native to the Andes Mountains, potatoes were introduced to Europe in the 16th century. They became the major constituent of many people's diets-especially in Ireland. Potatoes contain about 80 percent water, almost 20 percent starch, and 2 percent protein. One of the reasons potatoes are such an important food source is that they yield more calories per acre than any other major crop. If space is limited, potatoes will produce more edible mass than either cereals or legumes. And they also grow well in cool climates.

Fruits. Similar to leaves and stems, many fruits are relatively low in energy value, but are important sources of vitamins and minerals. They are usually more perishable than roots or stems, and are therefore more difficult to store and ship. Because of this, the juice is often extracted from fruits and bottled for shipment.

A fruit, you'll recall, is a mature ovary. We've already mentioned some types of fruits, such as snap beans, in the previous categories.

More than any other category of food we've discussed, fruits vary widely in their taste, size, shape, and nutritional value. Many fruits contain large amounts of water and few calories; others, like the date, avocado, banana, and fig, are quite concentrated sources of energy.

Fruits can be categorized by the type of plants they come from. For example, pepper, tomato, and squash-which we often refer to as vegetables-are all technically fruits harvested from herbaceous annual plants.

Some of the first fruits that students are likely to think of include perennial fruits of temperate climates. These include peach, cherry, apricot, and plum ("stone fruits," whose fruit is a drupe); pear and apple (pome fruits); grape, blueberry, and persimmon (true berries); and raspberry and strawberry (aggregate fruits or accessory fruits).

Tropical fruits include banana, the various citrus fruits, pineapple, avocado, guava, papaya, mango, breadfruit, date, kumquat, loquat, medlar, and tamarind.