Watercress is a perennial, hydrophytic plant (an aquatic plant whose renewal buds overwinter in water).

An excerpt from the article 20 facts about watercress

It is a plant with an ascending, angular, rooting stem, and alternate, unpaired leaves. Close clusters of tiny white flowers, with stalks that lengthen as they bloom, appear at the top of the branching stem. The plant blooms from June to September. The fruit is a curved scutellum (a dry, bursting fruit) up to 5 mm long. Watercress grows up to 60-80 cm tall.