Tatsoi (Brassica rapa subsp. Narinosa or Brassica rapa var. rosularis) is a leafy green vegetable commonly found in Asian recipes. Tatsoi was first cultivated in China in the 6th century, and was known to be nutritious and thought to have medicinal properties. It soon spread to Korea and made its way to Japan by the 20th century at the latest. In Japan it's known as tasai, while in China it can be called tat choy and jú huā cài, or chrysanthemum vegetable, because it grows into a chrysanthemum shape.