Lysimachia nummularia
A vigorous, fast-spreading evergreen ground cover that forms a flat mat only 2 to 4 inches tall, rooting freely at the nodes as it runs to 18 inches or more across. It performs best in full sun to partial shade with consistent, regular moisture, tolerating moist and even boggy soils that defeat many other plants. The rounded, coin-shaped green leaves carpet the ground densely and are accented by small, cup-shaped bright yellow flowers in late spring and summer. Use it as a lush lawn substitute in damp areas, to soften pond and stream margins, to spill over walls and containers, or to knit between stepping stones where light foot traffic occurs.