Brassica rapa var. perviridis

Komatsuna (小松菜（コマツナ）) or Japanese mustard spinach (Brassica rapa var. perviridis) is a leaf vegetable. It is a variety of Brassica rapa, the plant species that yields the turnip, mizuna, napa cabbage, and rapini. It is grown commercially in Japan and Taiwan. It is a versatile vegetable that is cooked and eaten in many ways. The plant is also used for fodder in some Asian countries. The leaves of komatsuna may be eaten at any stage of their growth. In a mature plant they are dark green with slender light green stalks, around 30 centimeters (12 in) long and 18 cm (7.1 in) wide. It is most often grown in the spring and autumn, as it cannot endure extreme heat or cold for more than a short time. Although nowadays it's grown year-round in greenhouses....read more on Wikipedia.