Domestication of grain crops
Most of our annual crops were domesticated from annual ruderals. Annuals are plants that complete their life cycle and go to seed in one year. Ruderals are plants that grow on recently disturbed ground. By domestication, we refer to the change from collecting plants in the wild to cultivating them.
In the process of domestication of grain crops, humans selected for large seeds and non-shattering seed heads. Only a small disturbance such as a little wind will cause shattering seed heads to release the seeds once they are mature. In contrast, non-shattering seed heads must be thrashed to remove the seeds. Another feature selected for was lack of dormancy in seeds. All seeds in a batch of grain seeds will germinate immediately when exposed to misture and the temperature is favorable (e.g. above 10oC). For most weeds, however, only a fraction of the seeds will germinate in any one year (see Mechanical Control of Weeds).
The wild, weedy relatives are still important sources of genetic material for the domesticated crops. The Middle East, notably Anatolia in Turkey, and Ethiopia are centres of crop diversity for many cereals. There, domesticated cereals still interbreed with their wild weedy relatives.
A local roadside weed, Hordeum jubatum Most of the seeds have been released.
Barley, Hordeum vulgare, an important grain. Note the large retained seeds, and awned glumes that are similar to those in H. jubatum