Bidens pilosa, commonly known as hairy beggarticks or blackjack, is an annual herbaceous plant in the family Asteraceae. It is native to the tropical and subtropical regions of the Americas but has become widely naturalized in many parts of the world, including Africa, Asia, and Australia, often as a weed in disturbed areas, agricultural fields, and along roadsides.
The plant typically grows up to 1–1.5 meters in height and features erect, branched stems covered with stiff hairs, giving it a rough texture. Its leaves are opposite, pinnately divided, and coarsely toothed, with a hairy surface. The flowers are small, yellow, and arranged in compact heads typical of the Asteraceae family. The fruit is a distinctive achene with two to four needle-like barbed bristles (awns) that easily attach to animal fur or clothing, facilitating seed dispersal.
Bidens pilosa is known for its rapid growth and adaptability to various soil types and climatic conditions, which contributes to its success as an invasive species in some regions. It is considered a problematic weed in agriculture due to its competitive nature and potential to host pests and diseases affecting crops.
The plant has been used in traditional medicine across different cultures for treating ailments such as inflammation, gastrointestinal disorders, and microbial infections. Some scientific studies have investigated its phytochemical composition, identifying compounds such as polyacetylenes, flavonoids, and phenolic acids, which may contribute to observed bioactivities. However, its efficacy and safety for medicinal use require further rigorous clinical evaluation.
Ecologically, Bidens pilosa serves as a food source for certain insects and may play a role in soil stabilization in degraded areas, though its overall impact is often considered negative due to its invasiveness.
Due to its widespread distribution and taxonomic complexity, some sources recognize varieties or subspecies within Bidens pilosa, though the circumscription of these taxa remains subject to botanical debate.