(Jimmy of the Clue Crew shows a plant diagram on the monitor.)  Similar to a root, it's the botanical term for a thick, horizontal underground stem from which shoots develop into new plants
The Crossword Solver will often find clues used in the New York 
Times ... RHIZOME, Thick horizontal underground stem of plants such as the iris (
7) ... Plant such as the cactus or agave that grows in arid conditions, using its... [DOC] [TLE] Deeper Insights into the Illuminati Formula - orbit [PAR] The Monarch Programming is a foundation rock of the New World Order that 
when ...