离子芥（学名：Chorispora tenella）为十字花科离子芥属下的一个种。

Chorispora tenella is a species of plant in the mustard family known by several common names, including purple mustard, blue mustard, musk mustard, and crossflower. This mustard is native to Eurasia but is well known in other parts of the world, particularly in temperate regions, as an introduced species and a noxious weed. This is an annual herb reaching a maximum of half a meter in height and covered abundantly in sticky foliage. The four tiny flower petals emerge from a loose tube of sepals and spread into a corolla about a centimeter wide. The flowers are lavender in color and a field heavily infested with purple mustard can take on a distinct lavender wash. The plant has a strong scent which is generally considered unpleasant. The fruits are long upturned cylindrical capsules about 4 centimeters long containing round, reddish-brown seeds. This is a tenacious weed which can be troublesome in agriculture. It reduces yields in grain fields and when it is consumed by dairy cattle it gives their milk a bad taste and odor. This plant reproduces by seed, so any control method preventing the plants from setting seed is effective.