Confronting the Green Threat: An Updated Inventory of India’s Alien Plant Species

Alien plant species increasingly shape India’s ecosystems, yet national-scale assessments integrating all invasion stages remain limited. We compiled a comprehensive checklist of India’s alien vascular flora, documenting 1,022 wild alien species and 1,725 species including cultivated aliens, standardized using APG IV taxonomy and validated through global databases. These species consist of 164 families and 491 genera, with Asteraceae, Poaceae, and Fabaceae emerging as the most dominant contributors across invasion stages. Herbs constitute the largest fraction of the alien flora, while trees, shrubs, and climbers also contribute substantially, together showing strong growth-form biases in invasion trajectories. Most alien species originated from Tropical America, Africa, and Europe, with Tropical America contributing disproportionately to India’s invasive pool. Ecoregional assessments revealed South and North India as invasion hotspots, whereas Central, Northeast, and Island regions supported more distinct alien assemblages. Jaccard similarity analysis demonstrated a clear invasion continuum: casual species showed low regional similarity, naturalized species formed moderate clusters among adjacent regions, and invasive species exhibited high compositional convergence across distant ecoregions, indicating broad ecological tolerance and strong human-mediated connectivity. Chi-square tests confirmed highly significant associations (p < 0.001) between invasion status and growth form, native region, and ecoregion, underscoring the non-random distribution of alien taxa in India. This study provides the fully standardized, taxonomically updated, and ecoregion-resolved national synthesis of India’s alien flora. By integrating invasion stages, species traits, biogeographic origins, and spatial patterns, it establishes a robust foundation for risk assessment, prioritization, and evidence-based invasive plant management across India’s diverse landscapes.