Native to temperate regions of Europe, Asia and North America. Grows in cool, running water and will spread very rapidly if conditions are just right. The leaves have long been used as a spring tonic, to correct vitamin deficiencies.
Analysis shows high concentrations of vitamin A, C and iodine.
A native preparation involved simmering the fresh leaves in water and reducing down the decoction to a thick, black-green syrup. The dosage was one tablespoonful every morning for a week. Sow seeds in moist soil in pots in the early spring. Allow to grow until roots fill the pot. Then, transplant out to the edge of cool running water.