Zannichellia (common name horned pondweed)[2] is a genus of submerged aquatic flowering plant,[3] with threadlike leaves and tiny flowers.[3] It is fully adapted to an aquatic life cycle, including underwater pollination.[2]
These slender plants grow submerged in water. The leaves are usually oppositely arranged and long and narrow. They have stipular sheaths.[5]
The flowers are unisexual. The male flowers have a single stamen with a slender filament and anthers that are 2-4-thecous.[5]
The female flowers have a cup-shaped membranous perianth. There are usually four carpels with a single pendulous ovule in each ovary. The stigma is shield shaped with toothed margins.[5]
The fruit is usually made of four long, dry achenes. The seeds are pendulous with a sub-cylindric embryo. The cotyledonous end is folded on itself twice.[5]
The species of this genus are widely distributed and are found growing in temperate and tropical regions around the world.[5][1] They grow in brackish and salt water.[5]