Bearded darnel disguises itself as wheat. It poisons livestock and sometimes people. Probably the plant called tares in the Bible is bearded darnel. In the thirteenth chapter of Matthew, Jesus tells a parable about it.
The parable
A man plants a field of wheat, but an enemy comes and contaminates the crop with the seeds of tares. Tares looks like wheat when it is growing, but can be distinguished once it matures.
The weed seeds must be separated from the wheat, because they are toxic. But the landowner says not to pull up the tares yet, “…while you are pulling the weeds, you may root up the wheat with them. Let both grow together until the harvest. At that time I will tell the harvesters: First collect the weeds and tie them in bundles to be burned; then gather the wheat and bring it into my barn.” (This New International Version translation is from biblos.com, which offers translations and commentary.)
The point of the parable seems to be that it is sometimes impossible to tell good from evil in this world, so it is best to let God judge others.
The plant
Bearded darnel, lolium temulentum, is a common weed, found in fields and waste ground throughout the world, but particularly in the Middle East. It does indeed resemble wheat until harvest time. At harvest time, wheat may bend while tares remain erect, and the tares’ seed heads may attain a darker color.
Wheat is sown close together, and pulling up the tares would in fact pull up wheat as well.
Bearded darnel is a species of annual ryegrass, growing up to four feet high depending upon variety and circumstances. The spikelets contain four to eight seeds, arranged alternately on the main stalk. Each seed is about the size of a small wheat grain. Here is a description at Henriette’s herbal.
The poison
Bearded darnel poison, temuline, can actually kill people, and apparently does kill livestock on occasion; its effects can be quite severe. It produces “drunkenness” of a sort: staggering, impaired speech, trembling, vision defects, and stupefaction. Oddly, though, the ryegrass may not be what produces the poison.
The fungus
A fungus, endoconidium temulentum, lives in most bearded darnel plants. It is an endophyte, that is, a fungus that lives within the plant’s tissues without doing its host any harm. Though we think of fungus as an infection, this one is helpful to the plant, as explained by D. Andrew White, here.
The fungus produces the toxin that makes the plant poisonous to insects and herbivores. Thus, the symbiosis produces its own insecticide, protecting the plant from being eaten before it can reproduce. The plant, in return, protects the fungus, and carries it on in its seed line.
Though bearded darnel may not be good to eat or drink, it is an interesting example of mutualism, as well as an illustration of a moral precept.
