Although it has been cultivated for centuries, black mustard is now found throughout Greece as a tall yellow-flowered roadside weed. Along with other similar mustard plants, it is collected as a wild green or horta plant. The seeds can be ground and mixed with vinegar to make mustard and is the main ingredient of Dijon mustard. The hot flavour comes from the chemical, isothiocyanate; it is not present in the whole seeds but it formed when the tissues are damaged. The use of mustard oil is banned in the EU, as it can be poisonous, containing similar substances to mustard gas.