西洋菜（英文:Watercress），别名豆瓣菜、水蔊菜、水田芥等，是十字花科西洋菜属的一种植物。

多年生的草本水生植物。茎圆形，匍匐生长，茎有茎节，根很容易从茎节长出来（例如：有水份）。奇数羽状复叶，浓绿色卵圆形小叶，有辛香味；总状花序，白色小花；长角果，黄褐色种子很小。

Watercress is an aquatic plant species with the botanical name Nasturtium officinale. This should not be confused with the quite different group of plants with the common name of nasturtium, botanical name Tropaeolum.

Watercress is a rapidly growing, aquatic or semi-aquatic, perennial plant native to Europe and Asia, and one of the oldest known leaf vegetables consumed by humans. It is currently a member of the family Brassicaceae, botanically related to garden cress, mustard, radish and wasabi—all noteworthy for their piquant flavor.