They include the Emmers, and Durhams, as well as Einkorn, the most ancient known type of wheat, which basically was a wild plant that people domesticated at some point. They are very nutritious and sometimes less allergenic than modern wheat. However, they are lower-yielding and harder to thresh. They all have hulls that cling to the grain and require either specialized equipment or a certain amount of work to dislodge.
Many of these require lower fertility, less water, and other inputs than modern types. They have large root systems and are adapted to marginal conditions. They produce best with wider spacings where the roots can forage widely--typically 8 to 10 inches.