The artichoke is a root.
Why it is true
The artichoke is actually the unopened flower of a plant of the genus Cynara. The part we eat is the fleshy bracts and the heart of the flower, before the flower fully blooms.
Source: USDA
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This is the reading side of the site, so the answer is in the sentence above — that is the whole point of it. Test yourself works the other way round: the question comes on its own, and the fact and the explanation only appear once you have answered.