a perennating stem-originated organ formed above ground (Serebrjakov and Serebrjakova 1965); its distal part is covered by soil and litter or pulled into the soil by the contraction of roots; nodes bear green leaves, the internodes are usually short; the rhizomes bear roots and serve as a bud bank and storage organs; vegetative spreading is usually slow (up to a few cm. year-1), persistence of epigeogenous rhizomes differ considerably among species
