Bidens frondosa

Bidens frondosa is a North American species of flowering plant in the aster family, Asteraceae. It is widespread across much of Canada, the United States, and Mexico It is known in many other parts of the world as an introduced species, including Europe, Asia, Morocco, and New Zealand. Its many common names include devil's beggarticks, devil's-pitchfork, devil's bootjack, sticktights, bur marigold, pitchfork weed, tickseed sunflower, leafy beggarticks, and common beggar-ticks.

Habitat and range
Bidens frondosa grows best where there is ample soil moisture and sun, especially in areas where something has disrupted the existing plant community leaving bare ground. It can survive in water saturated soils, frequently found growing at the water's edge, in drainage ditches or on flood plains.

According to Plants of the World Online (POWO) the natural range of Bidens frondosa is recorded as the whole of the continental United States except for Montana as well as all of Canada except for Labrador and the three Arctic territories. The USDA Natural Resources Conservation Service PLANTS database (PLANTS) agrees with the natural range in America, but lists it as an introduced plant for Canada. POWO lists the areas of the world where it is growing as an introduced plant as all of Europe except for Greece, Ireland, Iceland, Russia, Sweden, and Finland as well as Turkey, parts of Russia, China, Tadzhikistan, and the Caucasus.

Ecology
The defoliating caterpillar of Hadjina chinensis, which is limited to Bidens species, has been observed on this plant.

Morphology
Bidens frondosa is an annual herb, usually growing to 20-60 cm tall, but it may reach 1.8 m. The stems are square in cross-section and may branch near the top. The leaves are pinnate, divided into a few toothed triangular or lance-shaped leaflets usually 6-8 cm long, exceptionally up to 12 cm. The inflorescence is often a solitary flower head, but there may be pairs or arrays of several heads. The head contains many orange disc florets. Most flower heads lack ray florets but some may have a few small yellow rays. The fruit is a flat black or brown barbed cypsela up to a centimeter long which has two obvious hornlike pappi at one end.

The barbed pappi on the fruit help it stick to animals, facilitating seed dispersal.

Invasive species
This plant is invasive in some parts of the world. In New Zealand it is classed as an environmental weed by the Department of Conservation. It is also weedy in its native range, occurring in pastures and fields and along roadsides.