Step 1: Define a perennial plant.
A perennial is a plant that lives for more than two years. It typically regrows each spring from its existing root system.
Step 2: Classify the vegetables listed based on their life cycle.
Artichoke: The globe artichoke is a true perennial from the thistle group, producing edible flower buds for several years from the same plant.
Celery: This is a biennial plant, meaning it completes its life cycle in two years, but it is typically cultivated as an annual.
Knol-khol (Kohlrabi): This is a biennial, usually grown as an annual.
Leek: This is also a biennial, typically grown as an annual.
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Therefore, the artichoke is the perennial vegetable among the options.