Bidens frondosa
Bidens frondosa is a North American species of flowering plant in the aster family, sunflower family. 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. and common beggar-ticks. Description. "Bidens frondosa" is an annual herb, usually growing to tall, but it may reach . 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 long, exceptionally up to . 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. Ecology. "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. The defoliating caterpillar of "Hadjina chinensis", which is limited to "Bidens" species, has been observed on this plant. 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.