CHARLES D. WINTERS / SCIENCE PHOTO LIBRARY CHARLES D. WINTERS / SCIENCE PHOTO LIBRARY
Corn seedlings. Corn is the most widely grown grain crop in the Americas, with 332 million metric tons grown annually in the United States alone. Approximately 40% of the crop -- 130 million tons -- is used for corn ethanol. Transgenic maize (genetically modified corn) made up 85% of the maize planted in the United States in 2009. While some natural strains of maize can grow 12 metres (39 ft) tall, most commercially grown maize has been bred for a standardized height of 2.5 metres (8.2 ft). Sweet corn is usually shorter than field corn varieties.
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