What is a rhizome?
The rhizome is a special type of underground stem that grows horizontally below (or sometimes above) the soil surface. Unlike roots, rhizomes have nodes, buds, and internodes, allowing the plant to send out adventitious roots downward and aerial shoots (stems and leaves) upward from each of their nodes.
This structure It is essential in vegetative reproduction of many plants, since a rhizome can divide into fragments, and each one, as long as it has at least one bud, can develop into a complete plant. Furthermore, rhizomes store reserves of water and nutrients, essential for survival in adverse times and for rapid regrowth the following season.
Many well-known species possess rhizomes, from ornamental plants prized for their flowering to various edible and medicinal species. The versatile and resilient nature of rhizomes makes them key elements in the biology of perennial and biennial plants.
Main characteristics of rhizomes
- Underground or horizontal stem, different from the root due to its structure with nodes and internodes.
- Ability to produce adventitious roots and aerial shoots from its nodes, facilitating asexual reproduction.
- horizontal growth and indefinite in many cases, which contributes to occupying large areas of land.
- Nutrient and water storage in the internal tissues to ensure the survival of the plant during adverse periods.
- Easy vegetative reproduction: Simply cut the rhizome into fragments with buds to obtain new plants.
- Essential part of the annual cycle of many perennial plants, which lose their aerial parts during the winter and sprout from the rhizome.
- Support function and anchoring to the ground.
Thanks to these characteristics, rhizomes constitute one of the main storage and propagation organs in the plant kingdom.
Differences between rhizomes, roots, tubers and bulbs
Rhizomes: As we have already seen, they are horizontal underground stems with nodes, buds, and internodes, capable of producing roots and aerial shoots. They store nutrients and water and also function as reproductive organs.
- Tubers: They can be thickened stems or roots (depending on the species), which also store nutrients, but generally have a more rounded or oval structure, without marked horizontal growth or the emission of aerial shoots from nodes like rhizomes. A clear example of a cauline tuber is the potato (Solanum tuberosum), while sweet potato and carrot are root tubers.
- Bulbs: They consist of a short stem base, surrounded by thickened leaves (cataphylls) that store nutrients. Example: onion (Allium cepa) and garlic (Allium sativum).
- Tuberous roots: They are roots that have thickened to store reserves, unlike rhizomes which are always stems. Example: the dahlia (Dahlia) or sweet potato (Ipomoea batatas).
The key differences between rhizomes and these other underground organs lie in their structure (stem versus root), their reproductive capacity, and the way they store nutrients and develop in the soil.
Classification and types of rhizomes
Rhizomes can be classified in different ways according to their morphology and growth pattern. The most commonly used classifications in botany are as follows:
According to branching and growth
- Sympodial rhizomes: They exhibit a growth pattern in which the apical bud stops growing after forming an aerial shoot, and growth continues from a successive axillary bud. This creates a segmented appearance, where each portion corresponds to an annual cycle or a shoot. Examples: Sansevieria thyrsiflora, Paspalum nicorae.
- Monopodial rhizomes: The apical bud grows indefinitely, while the axillary buds produce aerial shoots. This type of rhizome is characteristic of many invasive species or weeds, such as Sorghum halepense y Phyllostachys aurea.
According to the development of the internodes and the growth pattern
- Defined rhizomes: They exhibit limited growth, with short, thick internodes. Their apical bud dies after forming a shoot, so growth continues from lateral buds. This pattern favors the formation of clustered, compact plants. Example: arundo donax (Castilian cane).
- Indefinite rhizomes: They exhibit long internodes and potentially unlimited vegetative growth, extending over great distances. The apical bud remains active, allowing for continued growth. They are often associated with rapidly developing and invasive species. Examples: Sorghum halepense y Phyllostachys aurea.
Other classifications
- Fleshy rhizomes: with a large accumulation of reserves, with a thickened appearance. Example: canna indica.
- Thin rhizomes: fewer reserves, more oriented towards rapid plant expansion.
Functions and benefits of rhizomes
- Nutrient storage: They allow the plant to survive droughts, frosts or other adverse conditions, providing reserves for regrowth.
- Vegetative propagation: Division into fragments allows a single plant to quickly produce many identical plants, colonizing large areas without the need for seeds.
- Structural support: they anchor the plant to the ground, allowing the aerial parts to develop vigorously year after year.
- Invasion or competition capacity in the natural environment, since many rhizomatous plants can occupy the terrain efficiently, even compared to other plant species.
- Fast regeneration: Rhizomes provide an advantage in the event of damage, fires or mowing, as they can develop new shoots in a short time.
Examples of plants with rhizomes
Numerous plant species have rhizomes, both of ornamental, agricultural and medicinal interest:
- Lily (Iris spp.): thick, fleshy rhizome, common in gardens and valued for its showy flowers.
- Ginger (Zingiber officinale): edible rhizome used in cooking and traditional medicine.
- Turmeric (Curcuma longa): aromatic rhizome, base of the condiment.
- Bamboo (Phyllostachys spp.): very rapid growth based on very extensive monopodial rhizomes.
- Aleppo sorghum (Sorghum halepense): example of an invasive rhizome, difficult to eradicate.
- Castilian cane (arundo donax): defined rhizome, used in environmental restoration and gardening.
- Sansevieria (Sansevieria thyrsiflora): very resistant ornamental plant, with defined rhizomes.
- Convallaria majalis (muguet): thin, creeping rhizome, produces beautiful white flowers in spring.
- Canna indica: fleshy rhizome, wide range of floral colors in gardening.
- Zantedeschia (Calas): highly appreciated ornamental, fleshy rhizomes.
- Achimenes: indoor and outdoor plant, scaly rhizomes.
- Ferns: Most ferns have rhizomatous systems.
Even some dicotyledonous plants and species considered less evolved, such as ferns, have developed rhizomes for their growth and propagation.
How plants reproduce with rhizomes
Vegetative reproduction by rhizome It is one of the most effective ways to multiply plants. The process takes advantage of the presence of buds along the rhizome, each capable of producing a new plant. The basic procedure consists of:
- Cut the rhizome into fragments, ensuring that each section contains at least one bud.
- Plant each fragment in a suitable substrate and maintain moisture until they develop their own roots and shoots.
- This method is preferred in gardening and horticulture due to its high success rate and speed compared to seed propagation.
Furthermore, this mechanism allows the plant to sprout vigorously after adverse periods (cold, drought). In fact, many perennial species lose their aerial parts during the winter, retaining only the underground rhizome, ready to sprout new stems and leaves with the arrival of the favorable season.
Advantages and disadvantages of rhizome plants
- Advantages:
- High regeneration capacity in the face of damage or unfavorable environmental conditions.
- Efficient propagation of the species without depending on seeds.
- Effective storage of reserves, ensuring long-term survival.
- Ability to colonize new spaces quickly.
- Disadvantages:
- In some cases, they can behave like invasive weeds and are difficult to eradicate.
- Competition with crops or other species in gardens and natural spaces.
- In controlled gardening systems they may require specific management to prevent excessive spread.
Rhizomes in food and medicine
Many rhizomes are important in human nutrition and in traditional and modern medicine. Prominent examples include:
- Ginger (Zingiber officinale): widely used as a spice and natural remedy.
- Turmeric (Curcuma longa): basis of Ayurvedic medicine and food seasoning.
- Galangal: similar to ginger, essential in Asian cuisine.
- Rhubarb (rheum rhabbarbarum): edible rhizome used in baking and medicine.
In other cases, rhizomes may contain active ingredients for medicinal purposes, and may also be toxic, so it is essential to correctly identify the species before use.
Morphological differences between rhizomes, tubers, bulbs and stolons
- Rhizome: An underground or surface stem, with nodes, internodes, and buds, it grows horizontally. It stores reserves and can sprout and root. To learn more about its types and characteristics, you can visit What are rhizomes?.
- Tuber: thickened stem or root, without horizontal growth, with mostly grouped buds ("eyes" in the potato), stores mainly starch.
- Bulb: A very shortened underground stem, surrounded by modified leaves, stores reserves and is generally rounded. Example: onion, lily.
- Stolon: creeping stem, generally superficial, which roots at the nodes when it touches the ground, forming new plants (example: strawberry).
These differences allow each structure to be clearly identified when studying a plant or when performing vegetative multiplication in gardening and agriculture.
Rhizomes and the life cycle of perennial plants
En perennial and some biennial plantsThe rhizome is the organ that allows plants to survive adverse seasons. These plants lose their aboveground leafy parts (leaves and stems) during cold or drought, retaining the rhizome underground. Thanks to the stored substances, the rhizome can sprout vigorously when favorable conditions return, restarting the vegetative and reproductive cycle year after year.
This mechanism ensures the survival of the species and facilitates its propagation, as each rhizome fragment can give rise to a new plant. Therefore, rhizomes are fundamental to the ecology of many ecosystems, allowing for rapid colonization of spaces, regeneration after disturbances, and the persistence of native flora.
Uses of rhizomatous plants in gardening and agriculture
- Ornamental gardening: Many spectacular flowering plants (lilies, canna, calla lilies, iris) are grown from rhizomes due to their ease of multiplication and hardiness.
- Edible crops: Rhizomes such as ginger, turmeric or rhubarb are indispensable in the kitchen and food industry.
- Erosion control: Some rhizomatous species, such as cane and bamboo, are used to fix soils and prevent erosion.
- Traditional and modern medicine: Several rhizomes provide active ingredients for medicines and natural remedies.
- Environmental recovery and restoration: Rhizomatous species are ideal for their ability to regrow and spread rapidly.
