Stachys affinis, the Chinese artichoke, knotroot, artichoke betony, or crosne, is an herbaceous perennial plant of the family Lamiaceae. Although its edible tuber can be grown as a root vegetable, it is a rare sight in the garden. From a cultivation standpoint this is rather odd — the plant is easy to grow, requiring neither staking nor earthing-up. The reason that it is so unpopular is the nature of the tubers — small, convoluted and indented, so that it is the cook rather than the gardener or the family who finds this vegetable frustrating. The thin skin is of whitish-brown or ivory-white. The flesh underneath, under proper cultivation, is white and tender.
In China, the Chinese artichoke is used primarily for pickling. Its tuber is a part of Osechi cooked for celebrating Japanese New Year. Dyed red by leaves of red shiso it is called Chorogi after it has been pickled.
Specialist Chinese wholesalers are one place you will be able to buy Chinese artichokes.
There is a very comprehensive list of corms and tubers here