“darnel.” The Greek word is zizanion (#2215 ζιζάνιον) and it refers to the plant Lolium temulentum, or the Bearded Darnel. There are other varieties of Lolium, but they do not closely resemble wheat, and therefore are almost certainly not the plant referred to in the parable. The Bearded Darnel looks so much like wheat that it cannot be distinguished from it except by an expert, until the grain starts to form. The darnel grain is much smaller than wheat and dark brown. The seeds of the darnel were believed to be poisonous to men and animals (although not fowl). It has now been asserted by some botanists that it is not the seed of the darnel that is poisonous, but rather that it is easily susceptible to getting a mold that is poisonous (Harold and Alma Moldenke, Plants of the Bible, Dover Publications, NY, 1952). Nevertheless, the ancients, and even the modern Arabs, do not make any such distinction, and consider the seeds to be poisonous. The symptoms of eating the darnel include nausea, vomiting, diarrhea, convulsions, and sometimes even death. The roots of the darnel are quite extensive, and when it appears in a wheat field, become entangled with the roots of the wheat so that if anyone tried to pull up the darnel they would most certainly pull up the wheat also.
Using the translation “weeds” as many modern translations do misses much of the depth of the parable. People frequently “weed” their gardens, and it is not hurtful but even helps the other plants grow. Only by knowing that one cannot do that with darnel makes that part of the parable make sense. Also, the parable epitomizes “by their fruit you will know them,” because it is when the grain starts to appear that the darnel can be easily seen.