An Etymological Dictionary of the German Language/Rispe
Rispe, f., ‘panicle,’ from MidHG. rispe, ‘f., ‘branches, bushes,’ akin to OHG. hrispahi, n., ‘bushes’; of obscure origin. The derivation from OHG. hrëspan, MidHG. rëspen, ‘to pluck, gather,’ is not quite satisfactory.