In the Great Plains area (more specifically, tall grass prairie) the lowly Sunflower reigned supreme as a cultivated food source for native tribes. It was made into bread, among other things.

I'm on my second crop this year, and the yield of seeds is unbelieveable.
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Member of the toughest, meanest, deadliest, most unrelenting -- and ablest -- form of life in this section of space, a critter that can be killed but can't be tamed. --Robert A. Heinlein