Top grass radical (Kangxi #140
艸 in its 3-stroke compressed form) — the indexing radical. Anchors the original meaning:
菜 is anything edible grown from the ground — vegetables, greens, then by extension a dish made from them (
一道菜 one dish). The radical groups
茶 (tea),
花 (flower),
草 (grass),
蔬 (vegetable),
药 (medicine).