mustard - black
Black Mustard plant.
The active ingredient that gives Black Mustard it's bight is called Isothiocyanates, which is also found in Rocket, Cress and Horseradish.
Once the plant matures it's leaves are too large and pungent to be used in salad. So, except for the plants I want for seed, I usually pull them out well before they grow to full size.
As well as for salads I grow one or two Black Mustard plants each year to provide black mustard seeds for cooking.