The non‐native <i>Areca triandra</i> palm is a potential threat to the southwestern rainforests of Sri Lanka

The palm family is a major source of invasive plants because of their long history of introductions outside their native range in tropical and subtropical regions for their use as food and ornamentals. Areca triandra was introduced to Sri Lanka in 1867 through the Royal Botanic Gardens, Peradeniya, and has been grown as an ornamental for over a century. To assess its potential invasiveness, we applied an invasiveness assessment protocol. Population and reproductive characteristics were studied in Meethirigala and Yagirala Forest Reserves. In each location, stems &gt; 1 m in height were sampled and crown cover was assessed in three plots of 400 m 2 (20 × 20 m) and the ground layer &lt; 1 m height sampled through four 1 × 1 m quadrats within each 400 m 2 (total of 24 quadrats). Areca triandra accounted for 56–66% of stems &gt; 1 m height, 52–76% crown cover, and 64–77% of saplings and seedlings in the ground layer &lt; 1 m height. Clump formation was high with 30–51% having 2–7 stems, compared to single stems of 12–26%. Fruit production was prolific, 140–250 fruits per infructescence, and each clump of multiple stems producing 1–3 infructescences. This resulted in a total of 250–440 fruits per clump, translating up to 8000 fruits per 20 × 20 m plot; bright red, (one‐seeded) fleshy drupes attracted avian and mammalian frugivores, aiding seed dispersal. This species was colonized along the disturbed forest edges where it can compete with native species, exposing vulnerability of highly fragmented rainforests. This study shows that the species is naturalized in the southwest humid lowlands and can be considered a potential invasive, emphasizing the need for urgent actions to manage this species.