Rhubarb has been imported into Europe in the 17th century via the Silk Road. It originates from Siberia and Mongolia; Rha is the old name for the river Volga and barbarum the Greek word for barbarians. Rhubarb is a vegetable, at its best between April and July when the stems are young. The stems are a bit tart and can be used in sweet dishes, but also in oriental curries and Moroccan tajines. The tartness is caused mainly by the oxalic acid (just like spinach), which, if consumed in high quantities, binds calcium. Rhubarb combines well with ginger and lemon rind.