These ‘aliens’ are here to stay. As many as 471 plant species that are alien or exotic — not native to India — are ‘naturalised,’ for they can thrive in the country’s wildernesses by forming stable populations, says a recent report.
This list of naturalised exotic or alien species, ranging from the common guava ( Psidium guajava ) to prolific invasives such as lantana ( Lantana camara ), has been compiled in a recent study published in Biological Invasions , an international journal dedicated to the patterns and processes by which organisms invade ecosystems they are not usually found in.
Ecosystem altered
Naturalised species reproduce naturally in the environments they colonise. Invasive species do this so prolifically that they alter the workings of the natural ecosystems they colonise or invade. Lantana, for instance, replaces undergrowth and prevents native undershrubs and plants from surviving.
An international team — including scientists from the University of Delhi’s Centre for Environmental Management of Degraded Ecosystems (CEMDE), the Botanical Survey of India (BSI) in Kolkata, Uttarakhand’s Central Himalaya Environment Association and Andhra Pradesh’s Sri Krishnadevaraya University — collated information on alien plant species from several sources, ranging from online plant lists to old compilations of India’s national and regional flora.
Tamil Nadu leads
The team also developed the first lists of naturalised plants for each State; these lists reveal that 110 alien plants now naturally occur in more than 31 States in India. At 332, Tamil Nadu has the highest number of naturalised exotics, followed by Kerala (290), while Lakshadweep has the least (17).
The distribution across Indian States of over 20 of these naturalised species (in the list of 471) is unknown.
A majority of these naturalised plants are herbs such as the invasive Siam weed Chromolaena odorata , native to south and central America.
The new list shows that many exotic species are now part of our natural flora, said co-author of the study, C. R. Babu, Professor Emeritus, CEMDE.
“We have to worry about the invasive species among these,” he added over the phone. “The government needs to strengthen quarantine measures adopted before a plant is brought to the country. We have to stop planting exotics just because they are fast-growing.”
More than 13,000 plant species are now naturalised in ecosystems across the world due to human activity; many of these later turn invasive and impact local flora and fauna. Last year, a study identified India as one of the ‘hotspots’ of naturalised plant species and among the seven regions in the world that have the highest number of invasive species. The ENVIS Centre on Floral Diversity hosted by the BSI lists more than 170 invasive plant species in India.
