Hornworts & Thallose Liverworts    
(Hornworts - Anthocerophyta)

Vegetative Morphologies similar to those above are seen in Hornworts (Anthocerophyta) & Thallose Liverworts (Hepatophyta) and . Some of these have wide, flat spreading thalli which are translucent and chlorophyllous throughout. They may be only 1-2 cells thick at their margins.

Thallus means a sheet-like form which does not have any resemblance to typical plant organs like leaves, stems or roots. The Hornworts & Thallose Liverworts have thalli which resemble green algae. In some cases all of the cells contain chloroplasts and the marginal areas are only one cell thick.

Some display Marginal Growth like Coleochaete and have Chloroplasts that are similar to the Green Algae (Chlorophyta).

Drawing of Anthoceros Thallus. The meristematic cells are located along the margins. This produces a flat, circular organism. The outline is undulating due to localized differences in meristematic activity.
Anthoceros (Hornwort) Thalli. These are relatively small, flat organisms that can form mats. They live in wet environments. It is difficult to see the individual plants which make up this mat.
Thalli of Anthoceros: The red lines indicate the margins of the individual Thalli.
Unusual Thalli of Anthoceros grown in culture. The Margins are deeply indented.
Some Chloroplasts from Anthoceros resemble those found in certain Green Algae. Each cell has only one Chloroplast. They contain a Pyrenoid which occurs in the Chlorophyta but is not found in any other terrestrial plant.

Honworts have Symbiotic relations with Nitrogen-Fixing Cyanobacteria. Hornworts tend to be "Pioneer" organisms that can colonize open areas in wet enviroments. Their symbiosis contributes to this because Nitrogen is typically a "limiting element" in terrestrial ecosystems.