The relationship between aluminium and silicon accumulation in leaves of Faramea marginata (Rubiaceae).

•   The relationship between high aluminium (Al) and silicon (Si) levels in Faramea marginata was investigated and the hypothesis tested that the coexisting accumulation of these elements is associated. •   Mineral concentrations of Al, Si and calcium (Ca) were analysed in 30 samples by atomic absorption spectrophotometry and the spectrophotometric molybdenum blue method. Extraction patterns of Al and Si from leaves were compared with Melastoma malabathricum, rice (Oryza sativa), aluminium silicate, and silicon dioxide. The localization of Al and Si was studied using pyrocatechol violet staining of sections and fluorescent X-ray analytical microscopy. •   A positive correlation occurred between the Al and Si levels and both elements showed a similar distribution in leaf and stem tissues. The Al and Si elution patterns were similar to those of aluminium silicate. •   These results suggest the formation of an Al-Si complex in the shoot tissues of F. marginata, which may substantially contribute to the internal detoxification of Al.