Tagetes minuta or Mexican Marigolds are an introduced weed with an unusual history: they were imported into this country in horse fodder used by the British troops during the Anglo-Boer war over a century ago. They acquired the name Khaki weed as a reference to the uniforms of the soldiers.
The tiny flowers are like little bunches of Marigolds.
They are very strong-smelling plants and if they are harvested with animal fodder, it becomes contaminated and animals will refuse to eat it as it makes them ill. The smell is nauseating and doesn't wash off easily from your hands if you have to hand weed these out of a garden. Some people consider these plants useful as the smell is also repellent to insect pests and farmers allow them to grow and then plough them into the land before planting crops such as potatoes as to help reduce worm populations in the soil