Which of the following is NOT a common underwater weed?

Duckweed is recognized as a floating aquatic plant rather than an underwater weed. Unlike the other options listed, which are rooted plants growing below the water's surface, duckweed typically floats on the surface, forming a green mat that can obstruct sunlight and affect water quality.

Bushy pondweed, Eurasian water milfoil, and leafy pondweed, on the other hand, all inhabit the submerged zones of aquatic environments, and their growth patterns directly contribute to the dynamics of these ecosystems. Understanding the distinctions between these types of aquatic vegetation is crucial for effective management and control strategies in aquatic pest management.