An aerial root is a specialized structure that develops from the stem of a plant, growing above the soil or water. These roots are a type of adventitious root, meaning they form from non-root tissue, and they are common in many tropical plants, including those often kept as houseplants. They represent a remarkable adaptation that allows plants to thrive in environments where access to soil-based resources is limited.
The Unique Structure and Purpose of Aerial Roots
Aerial roots differ structurally from the typical subterranean roots that anchor a plant and absorb water. Many aerial roots, especially those belonging to epiphytes, are covered by a spongy, multi-layered epidermis called the velamen radicum. This outer layer is composed of dead cells that form a porous structure, functioning much like a sponge to rapidly absorb atmospheric moisture from rain, mist, or high humidity.
Beneath the velamen lies the exodermis, which contains specialized passage cells that regulate the transfer of absorbed water and nutrients to the inner cortex. This unique design allows the root to collect water quickly while minimizing water loss, offering protection against desiccation in the exposed environment. The velamen also provides mechanical protection and can assist in anchoring the plant to its substrate.
Three Primary Types of Aerial Root Function
Not all aerial roots serve the same purpose; their function is dependent on the plant’s natural habitat.
Prop/Support Roots
This distinct group grows downward from the stem or branches to provide additional anchorage and stability for large plants. For instance, the roots of banyan trees descend from the canopy, eventually reaching the soil to form what appear to be new trunks, offering immense structural support. This category also includes the stilt roots of mangroves, which help stabilize the trees in soft, muddy, and often flooded coastal environments.
Clasping/Climbing Roots
These roots are designed for physical attachment to a surface. Plants like Monstera and ivy use these small, strong roots to adhere tightly to tree trunks or walls, allowing the plant to climb vertically toward light. These roots secrete a sticky substance that helps them grip the rough bark or masonry, securing the plant as it ascends.
Absorptive/Epiphytic Roots
Exemplified by many orchids and air plants, these roots do not grow in soil at all. These roots hang freely in the air, using their velamen layer primarily to absorb water and dissolved nutrients directly from the atmosphere. In some orchids, these roots can even contain chlorophyll and perform photosynthesis, highlighting their specialized independence from the soil.
Practical Management: What to Do (and Not Do) with Aerial Roots
A common question for houseplant owners is whether to remove the exposed aerial roots. In almost all cases, you should not cut healthy aerial roots because they are actively performing a necessary function for the plant, whether it is absorption or physical support. Cutting a healthy root creates an open wound, making the plant vulnerable to infection and disease. If an aerial root is visibly dead, shriveled, or diseased, it can be carefully removed with sterilized tools to prevent the spread of pathogens.
Instead of cutting, a better approach is encouraging integration or redirecting the roots. For climbing plants, gently guiding the aerial roots toward a moss pole or other support structure allows them to latch on and fulfill their natural climbing function. For plants being repotted, aerial roots that are flexible can often be tucked into the new potting medium, where they may transition into more conventional roots to aid in nutrient uptake.
To keep exposed aerial roots healthy, especially for epiphytic varieties, it is often necessary to provide high moisture. These roots thrive in the high humidity of their native tropical environments, so a visible, healthy aerial root is often a sign the plant is seeking or benefiting from atmospheric moisture. Regularly misting the roots or using a humidifier can help maintain the necessary humidity levels, preventing the roots from drying out and ensuring the velamen can effectively absorb water.