A "rhizome" is a modification of a plant's main stem that serves as both a root system and a way for the plant to reproduce. Rhizomes grow underground.
Rhizomes have nodes, which are small swellings. These nodes produce both rootlets that go down into soil and collect nutrients and produce stems that rise up through the ground and form new plants.
Many gardeners are ambivalent about plants with rhizomes because even if the plants are wanted, they can become invasive. Plants with rhizomes include species of bamboo, lily-of-the-valley, irises, cannas, some types of orchids and asparagus. Some plants are grown specifically for their rhizomes, which are used in cooking. These include ginger, galangal and turmeric.