Wheat then would never be feasible because of the amount needed to be grown to be of use. Offered by Woodie . We need to maximize edible growth per unit growing area for a given minimum growing time period. This might lead us to fast growing plants that are totally edible, roots and all. This is assuming light is a constant during our comparison.
Edible weeds become a consideration.
No hybrid problem and plenty of availability of seeds. Offered by Mike . Just musing here, but it seems that the beet plant is a good candidate. It grows well in all soil types. It will get along okay in shady areas.