Bidens pilosa is a species of flowering plant in the aster family. It is native to the Americas but it is known widely as an introduced species of other regions, including Eurasia, Africa, Australia, and the Pacific Islands. Its many common names include black-jack, beggar-ticks, cobbler’s pegs, and Spanish needle.
Bidens means two- toothed, describing the two projections found at the top of the seeds. A weed of gardens, woodlands, and waste areas, a person who brushes against it will end up covered in the burs and need to pick them off one by one.
The plant may flower at any time of the year, but in temperate regions it blooms mainly in summer and autumn. Flowers are borne in small heads on relatively long peduncles. The heads bear about four or five broad white ray florets, surrounding many tubular yellow disc florets.
^ Danaus chrysippus chrysippus [Plain Tiger butterfly]
Bidens pilosa flowers are nectar source for butterflies and honey-bees.