India's online plant trade may be an overlooked pathway for invasive species, study finds

Online plant trade in India carries invasive species risk, study finds

Lantana camara, one of the world's 100 worst invasive species, was brought to India in the 19th century as an ornamental garden plant. It now occupies 40% of India's tiger habitats. But a new study suggests Lantana is far from the only example of an ornamental plant turning into an ecological problem.

The study, published in the journal Environmental Conservation, examined India's online ornamental plant trade and found that the majority of plants sold online are alien species, many of which are known to be invasive or naturalised in other countries. According to the study, 57 species already declared invasive in India were available for purchase online, including Lantana camara and the highly-invasive Parthenium hysterophorus.

Invasive alien species are recognised as one of five major drivers of global biodiversity decline. "They outcompete our native species and the cost is enormous," said Kesang Bhutia, the study's lead author and a graduate student at Ashoka Trust for Research in Ecology and the Environment (ATREE), Bengaluru.

Bhutia compiled an inventory of 1,856 ornamental species sold online using data from three of India's largest online plant retailers that ship nationwide. Of these, 1,371 species (over 70%) were alien species, outnumbering the 480 native species on the list. Cross-checking against global databases showed that 327 species were invasive elsewhere, while 639 had naturalised outside their native ranges.

Among the invasive species found listed for sale were the common water hyacinth (Pontederia crassipes), bitter vine (Mikania micrantha), and mesquite (Neltuma juliflora). These species are known to cause significant ecological harm in various parts of the world.

"What was particularly alarming is that species already known to cause ecological harm in India are still easily purchasable and deliverable to homes; there's practically no barrier between 'known invasive' species and adding them to your cart," said Aravind NA, Senior Fellow at ATREE and the study's supervising author.

The e-commerce pathway

Aravind and his colleagues highlight that online retail presents an important but underexamined pathway for potential invasions. Unlike traditional imports, e-commerce often bypasses biosecurity checkpoints, as no quarantine inspections exist for plants shipped domestically by courier. This means that plants can be delivered directly to homes across the country without any oversight.

Aravind explained that e-commerce increases the geographic spread of propagule pressure—the number of individuals of a species that are released into an area—and the number of escape attempts a species makes. As the gap between identifying a species as invasive and allowing it to be sold nationwide persists, propagule pressure and geographic spread continue to grow, making post-establishment control costlier than prevention.

"Online retail presents an important but underexamined pathway for potential invasions," Aravind added.

The scale of the issue is not limited to India. Nearly three-fifths of the world's seed-plant species, including over 500 invasive species, are traded daily through platforms like eBay. Studies in Australia and the US have documented regulated and invasive species being sold despite biosecurity policies. Aravind observed, "In India, where plant trade regulations are less strict, the situation is arguably more vulnerable to this issue than in countries with more rigorous controls."

A systemic issue

The researchers note that the prevalence of alien species in online trade indicates a systemic issue, as the market centres around exotic, fast-growing, and easily propagated plants that tend to have invasion-prone traits. "Not all alien plants are a threat. There is a continuum," explained Bhutia. A newly-introduced plant cannot survive without human care. Some escape cultivation, enter native ecosystems and naturalise, reproducing independently. Others can go further to become invasive.

Less than 10% of introduced ornamental species escape cultivation, but the sheer volume of the ornamental plant trade contributes significantly to the spread of potentially invasive species. The study found that herbs were the dominant life form among the inventory's native, alien and invasive taxa.

Most alien species in the inventory originated from Southern and Northern America, possibly due to climatic similarities with India allowing them to easily establish. Bhutia explained, "The rationale behind it is that a species problematic in one area can be problematic in another which has similar climatic conditions." Apart from similar climatic conditions, another key indicator of an invasive species' invasiveness is its history of being a common metric used in Weed Risk Assessments globally.

Methodology and risk categories

The authors determined each species' native range using the Plants of the World Online database. They cross-checked the inventory against the ILORA, GRIIS, and GLONAF databases, categorising species based on invasion risk. A high-risk group of 39 species was identified, along with a moderate-risk group of 239 species—species recorded as invasive in other countries but not yet naturalised or invasive in India. Only two species naturalised in India and elsewhere but not invasive globally were identified as low-risk.

Aravind clarified, "This tool functions as a screening method, not a prediction," adding that it has a "solid precedent" in question. The authors suggest the lists be used to prioritise species for thorough risk assessments.

The study draws on the observation that more than half of the alien species recorded globally since 1950 had never been documented as established anywhere until they first appeared. This underscores the importance of early warning systems.

Experts weigh in

Mam Singh, Principal Scientist at ICAR-Indian Agricultural Research Institute, who was not part of the study, noted that "a lot of ornamental plants are coming in through high-tech nurseries and overseas imports." She added, "Customers always want something new, which may not be suitable for the local environment."

Anzar Khuroo, professor of Botany at the University of Kashmir, stated that traits like high seed output and resistance to herbivory that make ornamental plants easy to cultivate often help them naturalise and spread as invasive. He called the study a "valuable contribution" and noted, "Although alien plant inventories in India have been assembled over the last decade, a list specifically focusing on those alien plants traded online for ornamental use was lacking for the country."

Khuroo cautioned that alien species posing high risk in India's warmer tropical areas may not pose the same risk in temperate colder regions, and recommended that future studies assess regional applicability as well.

Regulatory gaps and recommendations

The study highlights a significant regulatory gap. No country-specific Weed Risk Assessment framework currently exists in India. The Plant Quarantine (Regulation of Import into India) Order, 2003 lists 57 quarantine weed species, of which only one (Anthemis cotula) is recognised as invasive by ILORA. Aravind observed a "striking mismatch between the regulatory list and the species actually known to be problematic domestically."

As per existing regulations, any planting material imported into India must be contained and monitored in post entry quarantine facilities for some months to ensure it is not harmful to public or environmental health. However, Singh added that on-ground monitoring needs to be more strictly enforced.

The study suggests a blacklist-based ban on species confirmed invasive in India, a measure the authors describe as cost-effective. Other proposed measures include opt-in risk labelling, promoting native alternatives and implementing a certification model like California's PlantRight programme. Singh said, "These are all very feasible" from an industry perspective.

Bhutia said, "The knowledge is there. How to merge that knowledge with regulations would be the next step." The study calls for the development of an "early warning mechanism" to minimise risks, as noted by Khuroo.

The databases the study relies upon possibly underestimate the threat, as pointed out by Bhutia, and the study only assesses what is available for sale, leaving the causal link between online sale and new invasions in India still to be traced. Nevertheless, the findings suggest that India's booming online plant trade could be an overlooked pathway for invasive species, with potentially serious consequences for biodiversity.