An Etymological Dictionary of the German Language/Rhabarber
Rhabarber, m., ‘rhubarb,’ ModHG. only, from Ital. rabarbaro, Fr. rhubarbe; also earlier ModHG. Rhapontif, from Fr. rapontique. The word is based on the MidLat. ra-, reu-ponticum, -barbarum, also radix pontica, -barbara, ‘a plant growing on the banks of the Volga.’