Which tiny, floating, rootless plant appears as nearly green specks on the water surface?

Watermeal is the correct answer because it is characterized by its tiny, floating, rootless structure that resembles small green specks on the water's surface. This aquatic plant is one of the smallest flowering plants in the world and is often found in freshwater bodies where it can spread quickly, covering the surface.

In contrast, duckweed, while also small and floating, typically has a larger size and can be easily distinguished from watermeal due to its distinct appearance. Big floatingheart and giant duckweed are larger aquatic plants and have more noticeable features such as broader leaves and roots that can be submerged or extend down into the water. Watermeal's unique size and lack of roots set it apart, making it an easily identifiable aquatic weed under certain conditions. Understanding these characteristics helps in accurately recognizing and distinguishing aquatic plants, which is crucial for effective weed management and control practices.