Underground stems and/or roots, often perennating [imprecise term, not recommended];
Rhizome, dorsiventral stem on or below ground sending out rootlets and distally leaves.
That portion of the stem where it joins the root.
The understock of a grafted plant; the base of a perennial where the roots grow.
The erect underground stem and roots of a perennial plant; also used as a general term for any root system.