in botany, a genus of the hexandria polygynia clasps. The characters of the alisma are these. The calyx consists of three pieces or leaves; the flower has three petals; and the seeds are numerous. There are seven species of this plant, viz. the plantago, or great water-plantain, which grows in all the marshy parts of this country; the ranunculoides, or lesser water-plantain; the natans, or creeping water-plantain; the damasonium, or star-headed water-plantain; all of which are natives of Britain: the flava, cordifolia, and subulata, are natives of America.