Lysimachia nummularia aka Creeping Jenny

Lysimachia nummularia is known as creeping Jenny or moneywort. This perennial belongs to the primrose family, Primulaceae. Its native range spans Europe, southwestern Siberia, and northwestern Turkey. It is native to Britain and Ireland. People introduced it to North America as a ground cover. It now grows wild in parts of that continent. It inhabits damp grassland, stream banks, pond edges, and roadside ditches.

The plant makes a low mat of green, branching stems. Most garden plants reach 0.17–0.33 feet (0.05–0.1 metres) tall. They spread 1–2 feet (0.3–0.61 metres), then may grow farther. RHS gives a broader height range, reaching 1.64 feet (0.5 metres). Stems form roots wherever their leaf nodes touch soil. Slender rhizomes also help the plant spread. The smooth leaves grow in pairs along the stems. They are green and round, sometimes with a heart-shaped base. Their edges have slight ripples but no teeth. Small red or black gland dots mark some leaf surfaces. Sources describe the foliage as deciduous or partly evergreen.

Yellow flowers appear from May through August. Each cup-shaped bloom grows where a leaf meets the stem. Most flowers grow alone, though some appear in pairs. Five petals bear small red spots. The flowers stand out against the low green mat. Small, dry capsules follow the blooms. These round or egg-shaped fruits split to free their seeds.

Grow creeping Jenny in sun or partial shade. Afternoon shade suits it in the St. Louis area. It grows best in moist, fertile soil rich in humus. It accepts clay, loam, sand, and several soil pH levels. Wet soil and brief flooding do not trouble it. It also tolerates some dry spells, though leaner soil slows spread. Its USDA hardiness range is 3–9; RHS rates it H6. Gardeners can raise plants from seed or divide established clumps. RHS states that it needs no pruning.

It can cover banks or trail over walls and container edges. It also suits pond margins where spread poses no threat. Near lawns and borders, its growth can become hard to control. It can crowd out native plants and is invasive in some regions. Check local restrictions before planting it outdoors. Serious pest problems are uncommon, but rust and leaf spots can occur. PFAF records tea made from its leaves and flowers. It also records traditional medicinal uses and no known hazards. That hazard record does not establish safety for every use.