in botany: A genus of plants belonging to the class of hexandra, and order of trigyna; and in the natural system ranging under the fifth order, Tripetalidae. The calyx is triphyllous; the petals are three; there is no style; the capsule opens at the base. There are three species; of which the palustre and maritimum are British.

1. Palustre, or arrow-headed grass, has an oblong trilobular capsule. The stalk is simple, eight or ten inches high; the leaves long and narrow; the flowers are greenish, and grow at the end of a long spike. It is frequent in moist ground.

2. Maritimum, or sea spiked grass, has ovate sexlocular capsules; the stalk is short; the spike long, and flowers purple. It is frequent on the sea-coasts. Linnaeus says that cattle eat these two species with avidity.