Chromolaena odorata aka Hagonoy

Chromolaena odorata is a perennial shrub in the Asteraceae family. Its common names include Siam weed and triffid weed. It comes from tropical and subtropical parts of the Americas. Its range spans South America, Central America, and the Caribbean. It also reaches southeastern North America. It grows in rainforest clearings and on river flats. It forms dense stands where gaps let sunlight reach the ground.

Young plants have soft stems that become woody with age. Early growth may die back when the growing season ends. Older plants form shrubs with long stems that ramble through nearby growth. In open sites, they reach about 10 feet [3 metres] tall. Forest plants can reach 23 feet [7 metres] or more. Their stems can also exceed 23 feet [7 metres] long. The growth can form a thick, tangled mass. Wind carries the light seeds, helping the plant reach new sites.

This species grows fast in warm, humid climates. It needs sun and suits tropical and subtropical conditions. Its best daytime temperature range is 20–35°C. Temperatures of −1°C or below may kill it. It grows in many soils but prefers good drainage. Its preferred soil pH is 5–6.5, though it tolerates 4–7.5. It favours areas with 2,000–4,000 millimetres of rain each year. Seed needs light to sprout, so shallow sowing suits it. Young seedlings stay small at first, then stem growth speeds up. A swollen root stores reserves and can produce new shoots.

People grow it for ornament and gather it for local medicines. It also has potential for use in early forest restoration. Yet its spread can outweigh those uses. It has become a serious weed in Southeast Asia, Africa, and Pacific islands. It quickly fills open ground, then fades as forest shade deepens. Reports describe its leaves as useful against some crop pests. These include weevils and nematodes. Trials with leaf mulch also report less disease in black pepper.

The leaves have seen occasional use to flavour soup. That limited food use does not establish general safety. Traditional medicine uses the leaves for fever, malaria, and skin wounds. These reports describe local practice, not proof that treatments work. The seeds contain alkaloids. Plant material added to flooded rice fields may kill fish. This hazard matters when weighing its use as green manure.