Key ingredient in some green smoothies (4)

I believe the answer is:

kale

(Other definitions for kale that I've seen before include "Crinkle-leaf cabbage" , "Type of cabbage" , "Crinkled-leaf cabbage" , "Cabbage in a lake" , "(Curly?) cabbage" .)

I've seen this clue in the USA Today.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.