Hi, One cactus that I grow produces underground tubers (I suppose they are tubers and not rhizomes, etc.). The root system reminds me of a Dahlia, but the enlarged roots tend to be long and cylindrical in shape. LINK: Opuntia macrorhiza and roots (pads shriveled for winter) http://members.aol.com/PlantStudy/omac/… Cordially, Joe Shaw
