Common Water-starwort / Mud Water-starwort
Minute petal-less green flowers with bright yellow stamens. Fruit as long as wide, winged lobes. Short-stalked bright-green oval leaves. Upper leaves in floating rosettes. Weak stems.
Frequent. Still or slow moving water, ditches, ponds, lake margins.
Also grows on mud and wet tracks.
Similar: Blinks, Montia Fontana