Appearance
''Bidens frondosa'' is an annual herb, usually growing to 20 to 60 centimeters tall, but it may reach 1.8 meters . 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 or 8 centimeters long, sometimes up to 12. 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.
Naming
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.Habitat
''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.
References:
Some text fragments are auto parsed from Wikipedia.