Not to be semantically confused with :
Swiss Treacle-mustard Erysimium rhaeticum,
Spreading Treacle-mustard Erysimiumrepandum,
Ball Mustard (Neslia paniculata),
Tower Mustard (Turritis glabra),
Hare's-ear Mustard (Conringia orientalis),
Chinese Mustard (Brassica juncea),
Black Mustard (Brassica nigra),
White Mustard (Sinapi alba),
Hoary Mustard (Hirschfeldia incana),
Russian Mustard (Sisymbrium ),
Hedge Mustard (Sisymbrium officinale),
Horned Mustard (Sisymbrium polyceratium), Garlic Mustard (Alliaria petiolata) [plants with similar names and probably similar hot taste but in differing genera of the Brassicacea family]
Easily mistaken with other yellow-flowered similarly narrow-leaved Brassicaceae such as :
Spreading Treacle-mustard (Erysimum repandum) (but that has larger petals, 6 to 10mm long [rather than the 3-6mm of Treacle Mustard]) or
Steppe Cabbage (Rapistrum rugosum) (but that has waisted fruits)
It grows in arable and waste places in scattered locations throughout most of the British Isles but is either rare or local in them except in Central, Eastern and Southern England where it is more abundant.
It doesn't appear to be used to make mustard for the dinner table but was formerly used in the 16th Century for insect and animal bites.
The plant contains toxic
Cardiac Glycosides of the
Cardenolide type which affect the heart.