Hornworts get their name from their horn-shaped spore capsules. These slender, upright capsules are where the plants make and shed their spores.
Hornwort is also the common name for the water weed Ceratophyllum demersum, an introduced flowering plant that has spread to many lakes and rivers in New Zealand.
Hornworts grow as a thick sheet of green tissue (a thallus). They are a small group of plants with about 100 species worldwide. Thirteen species of hornwort are known in New Zealand.
Differences between hornworts and liverworts
Although they look similar to thalloid liverworts, hornworts differ in four important ways:
- Most hornworts trap sunlight with only one or two massive chloroplasts in each of their cells (liverworts have dozens).
- Their chloroplasts can store carbon dioxide, a vital raw material for photosynthesis (liverworts cannot).
- They never have oil bodies in their cells (at least 90% of liverworts have oil bodies).
- Hornwort capsules continue to make and shed new spores for weeks (a liverwort spore capsule usually sheds all its spores within a few hours).
Hornworts are found in a variety of habitats, but are most abundant in damp places such as clay banks. Most settle on soil or rock, although some species prefer bark, and others overrun mosses and liverworts. Anthoceros species are often found on damp banks, while Dendroceros giganteus lives on swampy ground.