rhizome

noun

(Gr. riza: root) A subterranean, usually horizontal, somewhat elongate, root-like stem, such as found in many ferns, sending out leaves and shoots from its upper surface and roots from its lower surface; it is often thickened by deposits of reserve food material, and is distinguished from a true root in possessing buds, nodes, and usually scalelike leaves; it enables the plant to survive from one growing season to the next and in some species it also serves to propagate the plant vegetatively; it may be thin and wiry, as in couch grass, or fleshy and swollen, as in Iris. Sphenophytes spread via rhizomes, but also produce erect stems. Any prostrate or subterranean stem, usually rooting at the nodes and becoming erect at the apex. Compact upright underground stems, as in rhubarb, strawberry, and primrose, are often called rootstocks. Also rootstalk.