Pennywort

[Swede]

Water pennywort is a relatively small perennial plant that seldom exceeds 10 inches in height. Leaf petioles arise from creeping stems and attach to the center of the leaf. Leaves are round with bluntly rounded toothed margins, up to 2 1/2 inches in diameter. Flowers are borne on separate stalks as tall or taller than the leaves. Flowers are white to greenish-white somewhat inconspicuous with tiny simple flowers that arise from a single point on the stalk Pennywort can spread across moist soil or form floating mats on the water's surface. These mats can break off and form floating islands.

http://aquaplant.tamu.edu/database/emergent_plants/water_pennywort.htm