Abstract:
Mangroves are unique coastal ecosystems that heavily contribute to biodiversity, coastal protection and
climate resilience. Traditional classification of the species-rich mangrove communities along the coast
of Sri Lanka has relied heavily on plant morphology. The convergence and hybridization mechanisms
make many species superficially indistinguishable and create significant taxonomic confusion, which
affects biodiversity assessments and conservation workflows. To resolve these limitations, this study
presents the first comprehensive molecular phylogenetic classification of Sri Lankan mangroves using
the chloroplast ribulose-1,5-bisphosphate carboxylase/oxygenase large subunit (rbcL) gene marker.
Total Genomic DNA from 21 mangrove species (84 samples across the island) was isolated via
optimized CTAB and silica extraction methods, followed by PCR amplification and sequencing of the
rbcL marker. Phylogenetic reconstructions using Maximum Likelihood and Bayesian Inference
successfully placed our isolates in 13 genera across 10 families. The molecular phylogeny revealed the
status of Rhizophora anamalayana, clarifying that it is not a distinct species as previously debated but
a natural hybrid of R. apiculata and R. mucronata, exhibiting a 0.16% to 0.32% base pair difference
respectively in the rbcL marker with its reference specimen. Furthermore, Ceriops tagal specimens
from Trincomalee and Puttalam areas exhibited differences in morphology, while no significant
difference was observed (< 0.01%) in rbcL marker sequences in the phylogenetic analysis. In future
studies, it is essential to conduct comparative chloroplast genome analysis coupled with ecological
studies to obtain high resolution in molecular phylogeny for deep taxonomic insights and ecological
studies to enhance mangrove conservation, restoration, and climate resilience. This study underscores
that molecular phylogenetics is an indispensable tool for accurate species delimitation, natural hybrid
tracking, and establishing baseline data to guide future conservation and policy management.
