Alisma, a member of the plant family Alismataceae, is a herb commonly used in traditional Chinese medicine (TCM). The medicinal part of the plant is the dried root of Alisma plantago-aquatica. Alisma is also called mad-dog weed, water plantain, American
water plantain, or northern water plantain. It belongs to a different species from the edible plantain or cooking banana of the
Caribbean or the plantain that produces psyllium seed. The Chinese name for alisma is ze xie.

Alisma is a perennial plant that grows aggressively in shallow water and boggy spots in parts of Europe, North America, and northern China. Its leaves take different shapes depending on whether the leaves grow above or in the water. The plant rarely reaches a height of more than 30 in (0.9 m). There are several subspecies of Alisma plantago found throughout the world, but their medicinal uses are the same.