A tuber is a thickened part of the rhizome or underground stem of certain plants, enlarged as a starch storage organ. Some tubers are edible, such as those of potato, Jerusalem artichoke and jicama.
A corm is a short, thickened, vertical rhizome that stores starch.
Gilles_Deleuze and Felix_Guattari coined "rhizome" to describe theory and research that allows for multiple, non-hierarchical entry and exit points in data representation and interpretation.