An Etymological Dictionary of the German Language/Mangold
Mangold, m., ‘beet,’ from MidHG. mangolt, m.; its connection with Gold does not seem to be orig. If it is to be connected, as is usually done, with the proper name Managolt, the prim. meaning is ‘powerful ruler’ (manag and waltan; comp. Πολυκράτης), but scarcely ‘very gracious’ (Viel-hold). See Markolf. By what means the plant acquired this name can no longer be discovered. Others regard Mangold as Halsgold, ‘gold-neck’ (comp. Mähne); but mane-, ‘neck,’ is not found elsewhere in Teut.