A grass that looks very similar to wheat or rye. Scholars generally agree that the "weeds" mentioned in Matthew 13:24–30 are the annual or bearded darnel grass (Lolium temulentum). The seeds of darnel are much smaller than wheat or rye seeds, but it is extremely difficult to tell darnel apart from wheat or rye when the plants are young.
If darnel is not removed early but is left until harvest time, it gets cut down with the wheat. After cutting, the two plants are very difficult to separate. The seeds of darnel grass are poisonous, either because of natural chemicals they contain or because of a fungus that grows inside the seeds.