Explanations:Understanding the classification of aquatic plants is crucial for various competitive examinations, particularly those focusing on general knowledge and environmental science. Aquatic plants can be broadly categorized into three types: floating, submerged, and emergent plants. Each type has distinct characteristics and growth habits.
Floating plants are those that grow on the surface of water bodies. They can be either rooted or free-floating. Rooted floating plants have their roots anchored in the substrate at the bottom of the water body, while free-floating plants are not anchored and drift on the surface. Examples of floating plants include duckweed (Lemna minor), water hyacinth (Eichhornia crassipes), and water lettuce (Pistia stratiotes).
Submerged plants, on the other hand, grow entirely underwater. They are rooted in the substrate and have leaves and stems that are adapted to life underwater. These plants are crucial for maintaining water quality and providing habitat for aquatic life. Hydrilla (Hydrilla verticillata) is a well-known example of a submerged plant. It is an invasive species in many parts of the world and is known for its rapid growth and ability to form dense mats underwater.
Emergent plants are those that grow in shallow water with their stems and leaves above the water surface. They are rooted in the substrate and have parts that extend above the water. Examples include cattails (Typha spp.) and reeds (Phragmites australis).
In the context of the question, Hydrilla is a submerged plant, which means it grows entirely underwater and is not a floating plant. Duckweed and Pistia, on the other hand, are floating plants that grow on the surface of water bodies. Therefore, Hydrilla is the correct answer as it is not a floating plant.
It is important to note that the growth habit of plants can vary based on environmental conditions, but in general, Hydrilla is classified as a submerged plant, while duckweed and Pistia are classified as floating plants. Understanding these distinctions is essential for correctly identifying and classifying aquatic plants in various contexts, including competitive examinations.