Marsilea mutica variegata - Water Clover
Water clover is a delicate looking plant with floating leaves. It Can be invasive if not contained. Prefers part shade to part sun.
Nymphoides peltata - Floating Heart
Floating heart has glossy round leaves that look like a small water lily. It is a vigorous grower and produces yellow buttercup like flowers all summer. Can be very invasive as it grows from water borne runners so it is only recommended for lined ponds. It will grow in a variety of light levels full sun to full shade.