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Plants and Society, 3/e
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The Grasses

Chapter Summary

1. Grasses are members of the family Poaceae. The characteristic grains with large amounts of stored food are a vital food source, providing more than 50% of the calories consumed by the world’s population. Wheat, rice, and corn outrank all other plants as food sources for human consumption. Whole grains, with the bran and germ intact, are nutritionally superior to their refined counterparts, which contain only endosperm.

2. Wheat is one of the most widely cultivated crops in the world and is one of the oldest domesticated plants. Domesticated wheat had its origins in the Near East at least 9,000 years ago, and wild species of wheat can still be found in northern Iraq, Iran, and Turkey. Contemporary wheat species include diploid, tetraploid, and hexaploid species. The polyploid species arose through hybridization between diploid wheat and goat grasses. Wheat is nutritionally superior to other grains but still lacks some essential nutrients.

3. Corn, a New World native, was the dietary staple of many Native American tribes before the discovery of America by European explorers. Corn is an unusual grass, having separate male and female spikes. Many types of corn are cultivated, but all varieties are members of a single species, Zea mays. Corn was first domesticated in an area of central Mexico at least 5,500 years ago, but the origin of corn has been a botanical mystery. Although many botanists believe that teosinte is the ancestor of corn, other theories have been advanced.

4. Rice feeds more people worldwide than any other crop, and it is the only crop grown exclusively for human food. Oryza sativa is the main cultivated rice species, but over 20 species in the genus are known. Rice cultivation dates back 11,500 years and has been found in both eastern China and northern India. In most areas of the world, rice is cultivated in flooded fields or paddies, although it can be grown without flooding.

5. Other economically important grains include rye, triticale, oats, barley, sorghum, and millet. Triticale is a hybrid between wheat and rye that was developed to combine the hardiness and disease resistance of rye with the higher yield of wheat. Oats have always been considered a good food for horses but historically have had mixed acceptance as food for humans. In the United States oats were primarily eaten as only a breakfast food until the mid-1980s, when it was suggested that oat bran had cholesterol-lowering properties. Direct human consumption of barley is almost insignificant, but the importance of barley for livestock and in the brewing industry accounts for its tenth place among the world’s crops.

6. Grasses also provide nourishment for livestock in the form of forage. There is actually more land dedicated to forage crops than to all other crops cultivated, but much of this land is marginal and either too hilly, rocky, wet, or dry for other crops. Lawn grasses are indispensable components of landscaping designs and differ from crops in cultivation because plants are closely crowded together, maximizing competition between plants. Various species differ in tolerance to drought, temperature extremes, shade, humidity, and salinity and are, therefore, adapted to different climatic regions.