CHENNAI: The presence of Conocarpus trees on the median of National Highway 83 at Nallampalli near Pollachi has raised concerns among environmentalists and social activists, who have questioned how the controversial species continues to be found along public roads despite a Tamil Nadu government advisory prohibiting its cultivation and sale.
The issue has reignited the debate over the use of Conocarpus, an exotic ornamental tree, that has come under scrutiny for its ecological impact and potential health hazards. Activists have urged authorities to investigate the plantations and replace them with native trees in line with government directives.
Native to Africa and belonging to the Combretaceae family, Conocarpus was widely planted across India in recent decades as part of avenue landscaping and beautification projects owing to its fast growth and ability to thrive in harsh conditions. However, experts have flagged concerns over its impact on local biodiversity and public health.
A government-appointed expert committee had reportedly recommended to the Supreme Court in 2015 that the species be banned after studies highlighted ecological and health concerns in areas where it had been extensively planted, including along roadsides in Delhi. In January 2025, the TN Department of Environment and Climate Change issued an advisory banning the cultivation and sale of Conocarpus and directing authorities to gradually replace existing trees with native species.
The advisory instructed government agencies not to plant the species on forest lands, government properties and around residential areas, educational institutions, hospitals, hotels and resorts.
Speaking to DT Next, S Ravikumar, associate professor, Department of Botany, Presidency College, said, “Although introduced as an ornamental and avenue tree, Conocarpus does not adequately support native biodiversity. Reports have linked its pollen to respiratory ailments and allergic reactions. Ecologists have welcomed the State government’s decision to restrict the species and encourage the planting of native alternatives.”
Conocarpus was among several invasive alien species affecting Indian ecosystems. He also cited Parthenium, Eucalyptus and Seemai Karuvelam as examples of non-native plants that have spread extensively and altered local ecological balance. “These alien species often outcompete native vegetation and alter local ecosystems. Long-term efforts are required to control their spread and restore native biodiversity,” added Ravikumar.
The continued presence of Conocarpus trees along national highway medians has nevertheless left activists questioning whether agencies involved in roadside landscaping were adhering to the State’s advisory. When contacted, a senior official of the National Highways Authority of India (NHAI) said, “NHAI is not planting Conocarpus on our premises or highway medians because it’s banned. If our staff identify the species on highways, it will be removed.”
Environmental groups have called for a survey of roadside plantations across the State to identify and gradually replace invasive species with native trees that support biodiversity and comply with environmental guidelines.