Final answer:
The artichoke is a large, unopened flower bud with thick, green, compact scales and belongs to the Brassica oleracea species.
Step-by-step explanation:
The vegetable that is characterized as a large, unopened flower bud with thick, green, compact scales is the Artichoke. It belongs to the Brassica oleracea species, which also includes other familiar crops like cauliflower, broccoli, and Brussels sprouts. Artichokes have a thickened stem that is the part that is eaten.