Chromolaena odorata: Siam weed

Family: Asteraceae
Common name: Siam weed, Devil weed, Common floss flower, Armstrong’s weed, Baby tea, Bitter bush, Butterfly weed

A notorious weed that many countries are on the look out for, Siam weed is seen in almost all continents and countries. They can grow to a height of 2 meters when they are free standing; but when they can scramble on surrounding vegetation, they can grow to a height of 10 meters.

The stem is woody at the base, but tender and breakable towards the tip. Siam weed leaves are almost triangular with a flattened base near the petioles. Veins have a very interesting pitchfork pattern with three prominent veins that are clearly visible.

As the name ‘odorata’ suggests, the leaves have a distinct, pungent, strong aroma when crushed. Young leaves have a slight reddish tinge, and lighter green color; which turns dark green as the leaves mature.

The plant produces small hairy flowers that are light lilac, tending towards white color. Each bunch has about 10-35 flowers arranged so close, that the hairs of adjacent flowers look tangled with each other.

The seeds are small and narrow with a tuft of white hairs which help them to be dispersed by wind, water, animals and human clothing. Each Siam weed plant can produce over 80,000 seeds, this being one of the key reasons they are highly invasive.

Siam weed plants can survive extreme drought, water logging, poor soil, pollution, extreme temperatures and even fire damage. The dormant seeds in the soil will allow the plant to bounce back after damage by fire. Once the plants dry, they are a fire threat resulting in easy spreading of forest fires.

They are considered to be dangerously invasive weeds since they can suffocate small seedlings and crops with their fast-growing nature. It is toxic to cattle and can cause respiratory allergies in human beings. The leaves have some anti-inflammatory properties, and are crushed and applied to wounds for quicker healing.

Propagation is through seeds. They can also root where the stem nodes touch the soil.

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