What are the general characteristics of cereal grain crops?

They are grasses, and have large seed heads with very large seeds that can be easily harvested but don't shatter easily when brushed by or touched, like what happens with their wild cousins. They also have a very shallow root system, which enables them to be an annual, not a perennial. They have a shallow root system because 80% of their energy goes into seed production, not leaf nor root like the more native and pasture-type grasses do.