Bidens biternata aka Yellow Flowered Blackjack

Bidens biternata grows upright and lives for one year. It belongs to the daisy family, Asteraceae. Its native range spans the tropical and subtropical Old World. Records cover much of Africa, Asia, Australia, and the Pacific. It also grows in temperate parts of eastern China. It has spread beyond its native range into western Europe. Useful Tropical Plants calls it close to Bidens pilosa. The leaves help tell these two species apart.

Height figures differ, even within the same source. Useful Tropical Plants gives about 4 feet [1.2 metres]. Its full account gives an upper height of 5 feet [1.5 metres]. Some plants reach about 6.6 feet [2 metres]. These figures apply to the species as a whole. They do not give a tested range for garden plants. The sources give no firm measure for its width. Each flower has both male and female parts. Bees and hoverflies visit the flowers and help pollinate them. The evidence gives no clear time of year for blooms. It gives no detailed account of the fruit.

This plant grows in a wide range of wild sites. It grows in scrub, thickets, teak forest, and disturbed ground. It also grows in fields, gardens, and beside roads. Its habitat includes wet ground and the edges of streams. Records reach about 7,550 feet [2,300 metres] above sea level. Kew places it in a climate with dry seasons. PFAF says it needs light and prefers moist soil. It lists sand, loam, and clay as suitable soils. The soil may be mildly acid, neutral, or mildly alkaline. How well it copes with British winters remains unclear. Useful Tropical Plants says to sow seed where it will grow.

The sources chiefly describe a wild plant with local medicinal uses. They do not show a clear role as a garden ornament. PFAF notes that it is sometimes a weed in crops. Neither source lists a known food use or other practical use. Reports say people use leaf juice for eye and ear complaints. They also use leaves on skin problems and wounds. People have used the seeds against worms in animals, too. These records show past practices, not proof of safe treatment. Both sources report no known hazards. This does not prove it is safe for people or pets. The accounts give no facts on specific pests or diseases.