Bidens laevis aka Bur Marigold

Bidens laevis belongs to the aster family, Asteraceae. Its common names include bur marigold and brook sunflower. It is native to the Americas. NC State lists origins in the southern United States and several South American countries. These include Peru, Colombia, Venezuela, and northern Argentina. It grows in wet ground beside rivers and estuaries. In North Carolina, it occurs in coastal areas.

This upright plant can reach 6 feet (1.8 metres) tall. Its smooth, round stems branch and have a reddish tint. Heavy flowers and seeds can make the stems lean or flop. Glossy green leaves grow in opposite pairs along the stems. Each simple leaf has a lance shape and toothed edges. The leaves lack stalks and end in sharp points. Their wedge-shaped bases may join around the stem. Leaves measure about 0.17–0.5 feet (0.05–0.15 metres) long.

The flower heads have gold-yellow rays around brown disc flowers. Each head has about eight rays, though counts can vary. NC State gives a flowering season from June through October. It also notes that flowers can last until frost. Bees and butterflies visit the blooms. The fruit is a wedge-shaped achene with three or four angles. Its barbs catch on fur and clothes, helping it travel. Seeds provide the means for propagation and natural spread.

Choose full sun and soil that stays moist or wet. The plant also tolerates some shade during the day. It grows in sand, loam, or clay. Slightly acid to neutral soil suits it. Pond edges, stream banks, bogs, and marshes match its growing needs. NC State lists USDA hardiness zones 6b through 11b. Sources differ on its life cycle. NC State treats it as annual; Kew records it as perennial.

Mass plantings can add late-season color to wet garden sites. Native gardens, water gardens, and pollinator gardens suit this species. Its growth rate is moderate, but it can spread aggressively. Self-sown plants may crowd nearby plants in small gardens. Check its spread rather than assuming moderate growth means restraint. Possible pests include aphids, spider mites, and whiteflies. Powdery mildew and botrytis are also listed problems. NC State tags the leaves as edible but gives no preparation details. The supplied sources do not establish its safety for pets.