smartweed Persicaria (formerly Polygonum) hydropiper, an annual herb of Europe and Asia which owes its alternative name water pepper to its pungency and the fact that it grows in wet conditions. In Europe it has had only medicinal uses, but in Japan (where it is known as tade) it is consumed on a large scale as a garnish and accompaniment for many dishes.
The plants are usually marketed at the seedling stage, only a few days after the seeds have germinated. The leaves, which may be purplish or green, broad or narrow, according to the variety, are very pungent.
