Invasive plants that choke native species
Plants that are introduced into places outside of their natural range are called invasive plants. They are recognised as the second-worst threat to the world’s biodiversity, after habitat loss, and India is a hotspot for many invasive plants. Here are some of them:
Water hyacinth (Eichhornia crassipes)
A native of the Amazon basin of South America, the British introduced this aquatic plant into India for its beautiful flowers. It grows rapidly, suppressing native plants, blocking waterways and reducing dissolved oxygen in the water. Local communities use the roots of the plant to weave baskets. The plant can also be used to treat heavily-polluted waterbodies.
West Indian lantana (Lantana camara)
Originally from the American tropics, the Portuguese introduced this plant in Goa for its colourful flowers. Today, lantana is expanding across the world, and even penetrating India’s tiger reserves. It also impacts agriculture and crowds out native plants.
Carrot grass (Parthenium hysterophorus)
Also a native of the American tropics, Carrot grass invades a wide variety of landscapes. It successfully grows in pastures, farmlands, rice fields and forests. It causes disastrous loss of yield of crops, affects livestock and human health. It is believed to have entered India as a contaminant through imported wheat.
Siam weed (Chromolaena odorata)
An American native shrub, the Siam weed escaped from the botanical gardens of Dhaka in the 19th century and spread across the Indian subcontinent. Due to its dense growth, it prevents other species of plants from growing.
Wild tamarind (Leucaena leucocephala)
This nitrogen-fixing tree is one of the world’s worst invasive species. In India, urban municipalities promoted it for afforestation as it grows rapidly. The tree also provides firewood and fodder. Originating from Central America, it hinders the growth of native plants.
American rope (Mikania micrantha)
This Central American native creeper came to India after the Second World War to act as camouflage in airfields. Today, it has turned into one of the worst three weeds of tea plantations. The plant grows on any vertical support it can access and releases chemicals that inhibit the growth of other plants, including crops.
Black wattle (Acacia mearnsii)
Many species of acacia, including Acacia mearnsii, are endemic to Australia. Today, they are widely grown in India for timber and firewood. Acacia plantations in the Western Ghats are known to replace native plants of the Shola grasslands. In riparian zones, the acacia plants increase water loss.
Mesquite (Prosopis juliflora)
This is a thorny shrub native to Mexico, South America and the Caribbean. After the Europeans introduced it to Asia and Australia, this plant is now destroying grasslands and causing soil erosion in many parts of the world. In Kannada, it is called ‘ballari jaali’.
Crofton weed (Argentina adenophora)
A rapidly spreading weed in India, this plant from the daisy family is native to Mexico and Central America. Grown as an ornamental plant to start with, it is now an invasive species all over the world. It is known to be toxic to livestock.
Giant sensitive plant (Mimosa pigra)
This shrub, native to tropical America, resembles the touch-me-not plant but is larger. It is now an invasive species spreading through natural floodplains and pastures, converting them into unproductive scrublands. It is also known to block irrigation supplies to rice fields and reduce crop yields.