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Tatsoi (Brassica narinosa or Brassica rapa var. rosularis) (in Chinese: 塌棵菜, 瓢儿菜, 乌塌菜, or 塌古菜; and, in Japanese: タアサイ or 塌菜), also called spinach mustard, spoon mustard, or rosette bok choy, is an Asian variety of Brassica rapa grown for greens. This plant has become popular in North American cuisine as well, and is now grown throughout the world.
The plant has dark green spoon-shaped leaves which form a thick rosette. It has a soft creamy texture and has a subtle yet distinctive flavour.
It can be grown to harvestable size in 45–50 days, and can withstand temperatures down to –10°C (15°F). Tatsoi can be harvested even from under the snow.