tatsoi means: Also called’spoon cabbage’, tatsoi can be described as an Asian leafy green that has a mildly spicy flavor. You can use it in stir-fries and salads. (in Cooking Dictionary)

What else does tatsoi mean?

A plant from Asia (Brassica rapa subsp. rosularis) The mustard family has dark-green, spoon-shaped edible leaves. They grow in dense rosettes. (in Merlin Dictionary)