The biologist's ‘aquatic salad plant’ is actually a member of the cabbage family and although native to Europe and Asia generally had to be introduced to North and South America, New Zealand and the West Indies. It is now widely naturalised wherever the climate is not too hot for it. Virtually a perennial crop, with only a brief ‘off’ season in summer when other green salads are plentiful, watercress is now grown on the outskirts of all large cities and is at its best in autumn and early winter, when other greenstuffs are scarce.