A small dark green plant with round shaped leaves that imparts a peppery flavor to salads, sandwiches or garnishes. The watercress plant grows naturally along some streams but is grown hydroponically for commercial distribution.
Thankfully watercress is easy to find in most well-stocked grocery stores and at some farmer's markets.
This is an image of commercially hydroponically grown watercress. The leaves tend to be large and not as peppery as they are when you grow them in your garden.