Chinese keys, also called wild ginger or grachai in Thai, is a root in the same family as ginger. Although becoming hard to find in Bangkok, it is still quite plentiful in the markets of the north, where you'll most likely find it at the same stalls selling fresh ginger and cloud ear mushrooms. Chinese keys are probably the hardest spice to find outside of Thailand.
Chinese keys are long pencil thin roots that grow straight out from a single stem. The taste is pungent, more similar to galangal than ginger. Grachai is used in some curry pastes, although many now leave it out. It can also be used shredded in stir-fries, just like ginger. The root is also one of many Thai fruits and spices now used to make 'healthy' wines by several entrepreneurs around the north.