In planta phosphite concentrations were assessed in Adenanthos cuneatus, Astartea glomerulosa, Banksia coccinea, Dryandra tenuifolia, Eucalyptus recondita, Jacksonia spinosa, Lysinema ciliatum, Melaleuca thymoides and M. spathulata. At 5 weeks after phosphite application at rates of 36, 72 or 144 kg/ha, there was a significant correlation between in planta phosphite concentration and phytotoxicity symptoms for all species assessed. There was a linear relationship between in planta phosphite concentration and application rate for all species except B. coccinea. Phosphite concentrations differed significantly among species and application rates. The results indicated that in planta phosphite concentration were due to species-specific factors influencing phosphite uptake and retention. Variability in uptake and phytotoxicity symptoms among species has implications for the selection of appropriate phosphite application rates for disease control. Differences in the ability of species to metabolise, translocate or eliminate phosphite were not assessed and require further investigation.