A rhizome is a stem which grows on top of or under the soil, usually in a horizontal direction, and is key to the spread of rhizomatous plants. They may be slim or thickened and may bear leaves, roots, sideshoots and/or flowers.

Rhizomes are common to many perennial plants, including irises, asparagus, mint, bergenias, lily-of-the-valley, bamboos, orchids and ferns.

The propagation of rhizomatous plants is commonly done by dividing swollen rhizomes into segments and re-planting them or treating more slender, underground ones as root cuttings.