|The name "hornwort" refers to the long thin sporophytes which are embedded in the top of the plant and remain attached to it and continue to grow throughout its life. As all bryophytes, hornworts are gametophyte dominant.|
Other things which make the hornwort different when viewed under a microscope, are that the spaces between the cells are filled with mucilage rather then air chambers, where the cyanobacteria of the genus Nostoc live. The cyanobacteria fix nitrogen, which is used by the plant, in return for carbohydrates.
They also have a single, large chloroplast in each cell often completely enclosing the cell nucleus, which is unique among plants. This structure imparts a particular quality of colour and translucency to the body (thallus) of the plant. One chloroplast per cell is common in many algae.
The exact age of hornworts is not known, due to few fossil records having been found, but are believed to have evolved around 380 million years ago. There are about 100 species of hornworts, found worldwide in temperate and tropical regions on tree trunks, riverbanks, and other damp locations.