Although it has been cultivated for centuries, black mustard grows as a weed in many parts of the world, including Skopelos.  In early summertime, it fills roadsides, fields and olive groves with brilliant yellow flowers on tall branched stems. In winter and spring, it is collected as a wild green or horta plant; all parts of the plant are edible. It is not the leaves that are highly prized, but the tender tops of the stems with unopened flower buds, known as vrouves (βρούβες). 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.