Brassica juncea var. gemmifera, commonly known as Er Cai, is a cultivated variety of brown mustard characterized by its swollen, knobbly stem bases and tender lateral buds, which are consumed as a vegetable. The name Brassica derives from Latin refering to cabbages and related plants, while juncea means “reed-like” or “rush-like,” referring to the plant’s slender, upright growth in some forms. The varietal name gemmifera comes from Latin gemma (bud) and -fer (bearing), meaning “bud-bearing,” The Chinese name “Er Cai” (儿菜 or 二菜, depending on regional usage) loosely translates to “secondary vegetable” or “child vegetable,” referencing the clustered buds that grow from the main stem. It belongs to the family Brassicaceae and is native to East Asia, with its domestication and primary historical cultivation centered in southwestern China, particularly Sichuan and neighboring regions.

Historically, Er Cai has been valued in regional Chinese cuisines as a cool-season vegetable that stores well and bridges seasonal gaps in fresh produce availability. In traditional usage, it has been eaten fresh, stir-fried, braised, or added to soups, but it is especially notable for its role in fermentation and pickling, where its firm texture and pungent mustard flavor are well suited to lactic acid preservation. Er Cai continues to be widely used in Sichuan and Chongqing cooking, appearing in stir-fries with chilies, preserved preparations, and as a component of mixed pickled vegetables, while also gaining limited recognition in specialty Chinese markets outside East Asia.