Hornworts
| Hornwort Temporal range: 90–0 Ma Upper Cretaceous (but see text) to recent |
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| Phaeoceros laevis (L.) Prosk. | |
| Scientific classification | |
| Kingdom: | Plantae |
| Division: |
Anthocerotophyta Stotler & Stotl.-Crand., 1977 |
| Classes & Orders | |
see Classification. |
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| Synonyms | |
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Anthocerotae |
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see Classification.
Anthocerotae
Hornworts are a group of non-vascular plants comprising the division Anthocerotophyta. The common name refers to the elongated horn-like structure, which is the sporophyte. As in mosses and liverworts, the flattened, green plant body of a hornwort is the gametophyte plant.
Hornworts may be found worldwide, though they tend to grow only in places that are damp or humid. Some species grow in large numbers as tiny weeds in the soil of gardens and cultivated fields. Large tropical and sub-tropical species of Dendroceros may be found growing on the bark of trees.
The plant body of a hornwort is a haploid gametophyte stage. This stage usually grows as a thin rosette or ribbon-like thallus between one and five centimeters in diameter. Each cell of the thallus usually contains just one chloroplast. In most species, this chloroplast is fused with other organelles to form a large pyrenoid that both manufactures and stores food. This particular feature is very unusual in land plants, but is common among algae.
Many hornworts develop internal mucilage-filled cavities when groups of cells break down. These cavities are invaded by photosynthetic cyanobacteria, especially species of . Such colonies of bacteria growing inside the thallus give the hornwort a distinctive blue-green color. There may also be small slime pores on the underside of the thallus. These pores superficially resemble the stomata of other plants.
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