Which aquatic plant is characterized by its height and the final flower spikes it produces?

Purple loosestrife is recognized for its notable height, often reaching over 6 feet, and it produces dramatic flower spikes that can be seen from a distance. The pink to purple flowers bloom in dense clusters along the upper portions of the stems, creating a striking visual effect in wetlands and along shorelines. This plant is typically found in moist environments and can dominate areas when not controlled, thus impacting local ecosystems. Its growth patterns and flowering characteristics make it a distinctive aquatic plant compared to others that may be shorter or have different types of flowers.

In contrast, the other options lack the same height and flower spike characteristics. Watershield, while interesting in its own right, does not reach the same elevation, and its flowers are less showy. The American lotus, although it has large flowers, grows more as a floating aquatic plant and does not produce the tall flower spikes associated with purple loosestrife. Duckweed is a floating plant that remains small and does not produce noticeable flowers at all, making it quite different from the visually striking features of purple loosestrife.