Sigesbeckia orientalis aka Indian Weed

Sigesbeckia orientalis is an annual in the daisy family, Asteraceae. The RHS calls it eastern St Paul's wort. Its native range spans parts of Africa, the western Indian Ocean, Asia and Australia. It has also spread through many warm regions beyond its native range. People gather wild plants for medicinal use in Africa, Asia and South America. Some growers raise it for the same purpose.

The plant grows upright from a taproot. Spreading branches often start near the base. It usually reaches about 2 feet (0.6 metres) tall. Some plants reach 4 feet (1.2 metres). The whole plant has a strong, unpleasant smell. Reports also describe a sharp, bitter taste. In warm climates, it can bloom at any time of year. Flowering peaks in the rainy season. Humid weather can cause flowers to grow in excess. Insects pollinate the flowers.

This species grows from warm temperate regions into the tropics. Growth is best at temperatures of 10–27°C. It prefers sun and moist, fertile soil that drains well. Growers have raised it in both sandy and heavy soils. It is scarce in dry areas. Wild plants grow beside roads, in unused ground and in fallow fields. They also occur in young woodland and tea and coffee plantations. Some grow in forest shade. Most sites lie at low elevations, though some reach 6,890 feet (2,100 metres).

Growers sow seed straight into the growing site. Good conditions can allow two life cycles within one year. Its spread as a weed is a key concern. Several regions class it as invasive, including some Pacific islands. Its main documented role in cultivation is as a medicinal herb. Traditional uses include treatments for pain, fever and urinary complaints. These uses do not establish that it is safe or effective.

Young leaves have been eaten after cooking. The source says they need leaching to remove a toxin. Boiling also reduces their poor smell and taste. This makes the preparation warning important despite the source listing no known hazards. Seeds yield a fatty oil with possible uses in plastics. Oil from above-ground parts has been proposed for perfume. Leaf extracts also appear in skin-care products. Plant extracts have shown insecticidal effects against one crop pest.