Ludwigia L. species in Sri Lanka – An Update with Notes on Occurrence

Nimal R. Chandrasena

Keywords:

Primrose Willow, Ludwigia, Ludwigia adscendens, Ludwigia decurrens, Ludwigia hyssopifolia, Ludwigia grandiflora, Ludwigia octovalvis. Ludwigia perennis, Ludwigia peruviana

Abstract:

In Sri Lanka, the genus Ludwigia (Onagraceae) has not been thoroughly studied. With studies and plant collections made during 1978 through to 1990, I reported the occurrence of seven Ludwigia species on the island 1. Almost four decades later, in recent opportunistic surveys conducted in April and July 2025, all seven species were found occupying the same habitats as previously described. Three species, L. decurrens Walt., L. hyssopifolia (G. Don) Exell and L. perennis L. can still be found in rice fields. The first two are significant rice weeds. Of the two shrub-forming species, Ludwigia peruviana (L.) Hara is widespread on marshy land disturbed by human activities, while L. octovalvis (Jacq.) Raven can be found as a sporadic occupant of wet areas. Of the two sprawling aquatics, L. adscendens (L.) Hara is common in freshwater habitat in the low country. A name change is noted for the second creeping species (formerly identified as L. uruguayensis Camb.), which was previously limited to the Nuwara Eliya Gregory’s Lake environs. Its accepted name now is Ludwigia grandiflora (Michx.) Greuter & Burdet Hara). However, its abundance has declined after the lake’s recent rehabilitation. An eighth species, a popular ornamental, L. sedioides (Humb. & Bonpl.) Hara has also been recorded for Sri Lanka since 2006. In this article, I provide a key to identifying the seven Ludwigia species in Sri Lanka, based on floral and fruit characteristics, and notes on their occurrence and distribution in the Island to assist in any future revisions and studies.