Bidens cernua

Bidens cernua, commonly known as nodding beggar-ticks, nodding bur-marigold, or swamp beggar-ticks, is an annual plant belonging to the Asteraceae (sunflower) family. It is native to North America and Eurasia, often found in wetlands, marshes, along streams, and in other damp habitats.

The plant typically grows to a height of 1 to 3 feet (30 to 90 cm). Its leaves are lance-shaped and toothed, arranged oppositely along the stem. A key characteristic of Bidens cernua is its nodding flower heads. These flowers are usually yellow to orange-yellow in color and appear in late summer and fall. Each flower head contains both ray and disc florets. The ray florets are typically fewer in number than the disc florets.

After flowering, Bidens cernua produces seeds (achenes) with two to four barbed awns or bristles at the apex. These awns facilitate seed dispersal by attaching to animal fur or clothing, hence the common name "beggar-ticks." The plant's seeds are an important food source for waterfowl and other wildlife.

Bidens cernua thrives in moist, nutrient-rich soils and can tolerate standing water. It is considered a common and widespread plant in its native range. While generally not considered an aggressive invasive species, it can spread rapidly in suitable habitats.