The term “lily pad” is the common name for the floating leaf of a water lily plant, such as those belonging to the Nymphaea or Nuphar genera. The floating pad itself does not have roots; it is merely the leaf blade that rests on the water’s surface. However, the plant from which the pad grows is a rooted aquatic species, firmly anchoring itself to the substrate at the bottom of the water body. This plant’s root system is a complex, submerged structure.
The Structure of Rooted Water Lilies
The plant’s stability depends on a thick, horizontal stem called a rhizome, which is buried in the mud or silt at the bottom of a pond or lake. This rhizome is the central axis of the plant, storing energy and acting as the source for all other parts, including the roots. The roots themselves are typically fibrous and grow directly from the rhizome, spreading out to stabilize the plant within the soft sediment.
The floating leaves, or pads, are connected to the submerged rhizome by long, flexible stalks known as petioles. These petioles can extend for many feet, allowing the pad to reach the surface even in deep water. The roots do not grow from the petiole or the leaf; rather, the petioles and roots both originate from the same underground structure.
The rhizome is also a robust storage organ, accumulating carbohydrates and proteins to sustain the plant, particularly during dormant periods like winter. The entire structure—from the fibrous roots to the thick rhizome—is designed to withstand the forces of moving water and maintain a secure hold in the substrate. This anchored position is what distinguishes true water lilies from plants that simply drift on the water’s surface.
Unique Role of Aquatic Roots
Unlike the roots of terrestrial plants, which are primarily responsible for absorbing water and nutrients from the soil, the roots of water lilies have a modified function. Since the plant is surrounded by water, most of its water uptake and a significant portion of nutrient absorption occur through the stems and leaves. The roots’ main purpose is to physically anchor the entire plant structure to the pond floor, stabilizing it against currents and waves.
The submerged roots and rhizomes also require oxygen, but the mud and silt they are buried in are often low in oxygen, or anaerobic. To overcome this challenge, water lilies have specialized internal air channels called aerenchyma that run through the leaves, petioles, and rhizomes. This spongy tissue creates a low-resistance pathway that transports atmospheric oxygen captured by the floating leaves down to the submerged parts of the plant.
This adaptation allows the roots to survive in hypoxic conditions and provides a mechanism for gas exchange. The roots still absorb some nutrients, such as nitrogen and phosphorus, which helps to inhibit algal overgrowth in the water body. The roots’ capacity for nutrient storage also plays a major role in survival, supporting the plant’s growth at the beginning of the season.
Distinguishing True Lily Pads from Floating Aquatics
The common term “lily pad” should be reserved for the floating leaves of rooted plants like water lilies (Nymphaea and Nuphar). True water lilies are classified as rooted-floating plants because their roots are permanently embedded in the soil.
Other aquatic plants are truly free-floating and have an entirely different root structure. Species like duckweed (Lemna) or water hyacinth (Eichhornia crassipes) float unattached on the water’s surface. These free-floating plants possess small, adventitious roots that hang down into the water column, rather than anchoring into the substrate. Their hanging roots are designed specifically to draw nutrients directly from the surrounding water, making them highly efficient at absorption.
This difference in root structure is significant; the roots of a water lily are for anchoring and storage, while the roots of a free-floating aquatic plant are primarily for nutrient uptake. Understanding this distinction clarifies that while the pad itself is rootless, the plant it belongs to is deeply rooted.