The blackjack plant (Bidens pilosa) is a common annual herbaceous flowering plant found globally in tropical and subtropical regions. Often considered a weed due to its pervasive growth, it also holds significant traditional and practical uses. Its widespread presence makes it a subject of interest for gardeners and those exploring its diverse applications.
Identifying Blackjack Plant
Bidens pilosa is an erect, branched annual herb that can grow up to 1.8 meters tall. Its stems are typically four-sided, ranging in color from green to purplish. The leaves are oppositely arranged and vary in form, from simple to pinnately compound, typically having three to seven leaflets with serrated margins.
The plant produces small flower heads at the ends of its branches. These heads usually feature a yellow center of many disc florets, often surrounded by four to eight broad, white ray florets. Some varieties may have only disc florets. The most distinctive feature for identification are its seeds, known as achenes.
Achenes are blackish, narrow, ribbed, and elongated, about 1 cm long. They have two to five stiff, barbed awns at one end. These barbs allow the seeds to attach to clothing, animal fur, or feathers, facilitating widespread dispersal. Mature seed heads often form star-shaped burrs.
Where Blackjack Plant Thrives
Bidens pilosa originated in South America but has become widely naturalized across most pantropical and warm temperate regions globally. Its widespread distribution is largely due to its adaptability and reproductive potential. The plant thrives in disturbed areas, such as roadsides, agricultural fields, and gardens.
This plant prefers full sun, requiring at least six to eight hours of direct sunlight daily. It tolerates a range of soil types but performs best in well-draining, loamy soil that is moderately dry. It is tolerant to a wide pH range (4 to 9) and can withstand high salinities.
Bidens pilosa prefers temperatures between 15°C and 45°C, but its roots can endure temperatures as low as -15°C. A single plant can produce thousands of seeds per year, with seeds remaining viable for five to six years. Its rapid growth rate contributes to its invasive potential in many regions.
Uses of Blackjack Plant
Bidens pilosa has a long history of traditional use as both a food source and a medicinal plant. Young leaves and shoots are edible, consumed raw in salads, cooked as potherbs, or added to soups and stews. In some regions, fresh or dried shoots and young leaves are boiled and eaten as vegetables, while in others, fresh leaves are used to prepare teas.
The plant is a source of nutrients, including vitamin C, iron, and zinc. It also contains diverse compounds, including flavonoids, polyacetylenes, phenolics, and fatty acids, contributing to its various biological activities.
Medicinally, Bidens pilosa has been traditionally used for numerous ailments. It is well-documented for its anti-inflammatory, antimicrobial, and antioxidant properties. Extracts have been used to address inflammation, pain, and infections. Traditional applications include treating headaches, stomach ulcers, malaria, dysentery, and to support liver health.
Managing Blackjack Plant
Managing Bidens pilosa depends on whether it is viewed as an unwanted weed or a beneficial plant. To control its spread, preventing seed production is a primary strategy. Manual removal by hand pulling or hoeing is effective for smaller infestations before plants set seed.
Mulching can suppress growth by smothering young plants and preventing seed germination. Cultivation can also discourage establishment. For larger areas, mechanical removal may be necessary, though this can disturb the soil. Chemical control options exist but require careful adherence to product labels.
If cultivating Bidens pilosa for its uses, it is relatively easy to grow. It thrives in full sun and well-drained soil, with moderate watering. While fertilizer requirements are low, a balanced fertilizer can be applied sparingly. Propagation is straightforward from seeds sown directly after the last frost.