Water hemlock also has a large swelling at the stem base which water parsnip lacks. Characteristic plants include milk parsley, greater water parsnip and lesser reedmace. All water hemlock and poison hemlock are highly poisonous, but water parsnip is not. Water parsnip flowers are perfect (both male and female) and are self-fertile. Water parsnip has light green and glabrous stems with longitudinal veins and few branches. In the presence of added N03-N to the ground, water parsnip shows increased production.