Phenotypic leaf variation in Avicennia marina in tropical Australia: can discrete subpopulations be recognised in the field?

The geographic patterns of phenotypic variation in leaf morphology traits were studied in the mangrove Avicennia marina (Forsk.) Vierh. in tropical Queensland, Australia, to determine whether discrete subpopulations could be recognised in the field. Significant differences in the various leaf characters occurred among the sites, which were not explained by longitude or latitude, nor by inter-site distances. Hierarchical cluster analysis of the estimated site means showed no coherent geographical groupings of the sites, suggesting that site populations do not follow a differentiation by distance model. Principal component analysis showed that site groupings with consistent leaf morphological characteristics could be identified, suggesting the A. marina occurs as widely scattered discrete subpopulations, and that phenotypic structuring occurs over quite short (km) distances. Evidence from other studies suggests this phenotypic structuring reflects underlying genetic diversity, and it implies that a conservative approach to sourcing plant material for mangrove restoration projects would be appropriate.