The “blackjack flower,” Bidens pilosa, is a widely recognized plant found globally. Often considered a common weed due to its pervasive nature, this resilient species holds a significant place in various traditional practices. Its adaptability has led to numerous local names, reflecting its familiar presence.
Identifying the Blackjack Flower and Plant
Bidens pilosa is an erect annual herb, though it can sometimes behave as a perennial depending on the climate. The plant typically grows between 0.3 to 2 meters tall, featuring reddish-tinged, four-angled stems that can be simple or branched. Its leaves are arranged oppositely along the stem and are usually compound, consisting of three to five serrated, ovate to lanceolate leaflets. The terminal leaflet is often larger than the lateral ones.
The flower of Bidens pilosa is a small head, typically 5 to 12 millimeters wide, appearing solitary or in loose clusters at stem and branch ends. These heads commonly feature a yellow center of numerous tubular disc florets. Surrounding this, there are often four to eight broad, white, petal-like ray florets, 7 to 15 millimeters long, though these may sometimes be absent or small.
The most distinctive feature of Bidens pilosa, and the origin of its common name “blackjack,” lies in its seeds. These seeds, also known as “beggarticks” or “cobbler’s pegs,” are slender, black, four-ribbed achenes, 6 to 16 millimeters long. Each seed is tipped with two to five stiff, barbed bristles or awns, 2 to 4 millimeters long. These barbs allow the seeds to readily attach to clothing, animal fur, or feathers for widespread dispersal.
Habitat and Growth Habits
Native to tropical and Central America, Bidens pilosa is now naturalized globally in tropical, subtropical, and warm temperate regions. It thrives in disturbed soils and high sunlight, commonly invading gardens, agricultural fields, roadsides, pastures, and other open, disturbed spaces.
The plant is resilient, tolerating a wide range of soil types, from moist to moderately dry, and a pH of 4-9. It is a fast-growing annual, sometimes persisting as a perennial. A single plant can produce up to 6000 seeds per year, contributing to its rapid colonization. This prolific seed production and efficient dispersal make Bidens pilosa a persistent and competitive species.
Traditional Uses and Modern Perspectives
Beyond its weed status, Bidens pilosa holds significant traditional value as a food source and medicinal herb in various cultures. Its young leaves and shoots are consumed as a leafy green vegetable in parts of Africa and Asia. These tender parts are eaten raw, steamed, or added to soups and stews, and are sometimes dried. The plant is also considered a good source of iodine.
Traditionally, Bidens pilosa is used in herbal remedies for various ailments. Various plant parts (roots, leaves, seeds) are used for their reported antibacterial, anti-inflammatory, antimicrobial, and antioxidant properties. It is used to treat wounds, ulcers, ear infections, stomach disorders, and flatulence.
Modern research investigates these traditional claims, exploring Bidens pilosa’s bioactive compounds. Studies indicate its potential in managing diabetes (showing hypoglycemic and insulin-releasing activities in animal models) and its anti-inflammatory and antimicrobial effects, aligning with traditional uses.
Managing Blackjack in Your Garden
Managing Bidens pilosa in a garden depends on whether it’s viewed as beneficial or a weed. For control, manual weeding is effective, especially when plants are small. Remove plants before they produce seeds, as seeds remain viable for several years.
Thick mulch prevents seed germination by blocking sunlight. Regular cultivation discourages growth. Mowing at early stages prevents seed production and controls the species. Though a nuisance due to clinging seeds, Bidens pilosa can act as a pioneer plant in disturbed areas, contributing to soil cover and attracting pollinators.