Which plant is characterized by being free-floating and can be smaller than a pinhead?

The plant that is characterized by being free-floating and can be smaller than a pinhead is watermeal. Watermeal, which can be considered among the smallest flowering plants, typically measures less than 1 mm in diameter, making it even smaller than duckweed. It often forms dense mats on the surface of water bodies, contributing to its classification as a free-floating aquatic plant. While duckweed is also a free-floating plant, it is generally larger than watermeal and does not reach the extremely small size described in the question. Watershield and American lotus, on the other hand, are rooted aquatic plants and do not exhibit the same free-floating characteristics or size.