Koeleria macrantha: performance and distribution in relation to soil and plant calcium and magnesium

•  The reported sensitivity of Koeleria macrantha (Poaceae) to soil magnesium, resulting in its absence from South Wales dolomitic limestone, was examined here in relation to varying ionic Ca to Mg ratios, and by cultivation in different limestone soils. •  In a growth cabinet experiment, shoot and root Ca and Mg concentration and dry weight yield were determined for five edaphically varied populations of K. macrantha grown from tillers, over a range of Ca : Mg concentrations. The influence of relative concentrations of other nutrients was also investigated. In addition, K. macrantha plants were cultivated on Carboniferous, Magnesian and dolomitic limestone soils. •  Total plant Ca: Mg ranged from 0.3 to > 20 mille-equivalents. Optimal substrate ratios (from 25 : 1 to 0.1 : 1), and response to different concentrations of nutrients varied between the populations. Cultivation on dolomitic limestone soil produced the highest yields. •  The adverse effect on yields of all populations with low substrate Ca: Mg was much lower than predicted. Results suggest K. macrantha has a higher substrate Mg tolerance than other members of the Poaceae: its reported absence from the South Wales dolomitic limestone is unlikely to be due to soil magnesium sensitivity.