A rhizome is a modified plant stem that grows horizontally, typically beneath the soil surface. This subterranean structure is a specialized organ that allows certain plants to survive unfavorable conditions and reproduce asexually. By growing outward, the rhizome serves as a foundation for new shoots and roots, enabling the plant to spread and colonize new areas. This unique growth pattern dictates the characteristic propagation of many common garden, agricultural, and landscape plants.
Defining the Rhizome Structure and Function
The rhizome is botanically defined as a stem, which is made clear by its internal anatomy containing nodes and internodes. Unlike a true root, the rhizome possesses nodes, which are points along the stem where leaves, shoots, and roots originate. Small, papery scale leaves are often found at these nodes, which also house both apical and axillary buds capable of generating new upward-growing stems.
Adventitious roots emerge from the underside of the nodes, anchoring the stem and absorbing water and minerals from the soil. The rhizome’s primary biological functions are twofold: storage and vegetative propagation. It acts as a storage organ, accumulating starches, proteins, and other carbohydrates to sustain the plant through dormant periods, such as winter or drought. The stored energy reserves allow the plant to rapidly produce new growth when conditions improve. Furthermore, the horizontal growth is a form of asexual reproduction, allowing the plant to spread laterally and form genetically identical clones.
Common Edible and Ornamental Plants
Many economically important and widely recognized plants rely on rhizomes for their growth and survival. Among edible plants, the fleshy, knotty structures commonly sold as ginger and turmeric are, in fact, rhizomes, not roots. These underground stems are rich in the stored starches and oils that give them their characteristic culinary flavor and texture.
Asparagus also develops from a crown, which is a dense mass of rhizomes, with its edible spears being the new shoots that emerge from the buds. Hops, utilized in brewing, are another agricultural plant that uses rhizomes to establish extensive underground networks.
The world of ornamental gardening is filled with rhizomatous plants prized for their hardiness and ability to form dense displays. Familiar garden favorites like Iris, Canna lilies, and Daylilies all grow from thick, storage-rich rhizomes. Many species of ferns also possess rhizomes, which often creep along or just below the soil surface, sending up the characteristic fronds.
Ornamental grasses and bamboo are notable examples where the rhizome dictates the plant’s growth pattern. Running bamboo species, such as Phyllostachys, possess long, thin rhizomes that rapidly spread horizontally, allowing for quick colonization of a large area. In contrast, clumping bamboo species, like Fargesia, have short, thick rhizomes that grow in a tight, contained mass, resulting in a dense, non-spreading cluster of canes.
Managing Rhizomatous Growth
The spreading nature of rhizomes creates a significant challenge for gardeners and land managers, particularly with aggressive species. Plants with a “running” growth habit, like many grasses and bamboos, send out long rhizomes that can travel several feet in a single season before sprouting new shoots far from the parent plant. This aggressive spread is why running bamboo requires physical containment, such as a thick plastic barrier installed vertically in the soil, to prevent its escape.
The difficulty in eradicating these plants lies in the regenerative capacity of the rhizome fragments. Tilling or chopping the underground stem can inadvertently spread the problem, as each small piece with a node is capable of sprouting into a new plant. This fragmentation effectively multiplies the invasion rather than removing it.
Effective management often involves exhausting the plant’s stored energy reserves rather than just removing the above-ground growth. Repeatedly cutting down new shoots as they emerge forces the rhizomes to use their stored starches to regenerate, eventually depleting the reserves and killing the plant. For smaller, contained areas, the rhizome mass must be entirely dug out, ensuring no small fragments are left behind in the soil to resprout.