Root elongation of Geum rivale and G. urbanum grown in nutrient solution decreased as manganese concentration was increased above 25 mg dm−3, especially in G. urbanum. Prior exposure of roots to 25 mg Mn dm−3increased their capacity for subsequent elongation in manganese solutions, the effect of such pretreatment being most pronounced in G. rivale. G. rivale was significantly more tolerant of 50 mg Mn dm−3than G. urbanum. Efflux of potassium from root segments, used as a measure of membrane permeability, was significantly higher in G. urbanum than in G. rivale at this concentration. Tolerance of 50 mg Mn dm−3by progeny of hybrid individuals was generally related to morphological intermediacy, although there were some noticeable exceptions. Manganese tolerance of hybrids could not be consistently related to their known tolerance of waterlogging.