“Guinea corn” is a name for durra, a grain traditionally grown in Asia, the Middle East, Africa, and southern Europe. It was typically ground into meal and made into bread. It is also known as Indian millet, African millet, or pearl millet.
Guinea, now the name of a west African nation, is also a traditional term for the entire region of West Africa.
The photographer, Harry Marshall, notes:
A few weeks before this field of guinea corn would have been dusty and barren. But when the rains arrived guinea corn and other plants grew so fast you could note the progress daily.