Division Anthocerophyta: The Hornworts
The Anthocerophyta is a very small division composed of plants called hornworts. The hornworts are interesting to botanists because they are very similar to the green algae For example, their cells contain a single, large chloroplast. The group is referred to as hornworts because the shape of the sporophyte resembles a horn.
Figure 13. Structures of a hornwort. The alteration of generations is shown. The gametophyte plant attaches to the substrate by the rhizoids. The antheridium on the left contain sperm (shown in red) and the archegonium in the middle contains an egg (lime green with a red center). When fertilization occurs sporophytes are formed and grow into stalk-like projections. A close-up of the sporophyte is shown on the right. It has a large foot (shown in olive green) at the base acting as an anchor. There are then different types of cells forming the stalk including meristem, later initial cells, and sporogenous cells. In the center of the sporophyte is the columella (shown in dark green). Coming from the top of the sporophyte you can see yellow cube-shaped spores being released which then grow a horn-shaped projection called a protonema. These then grow into the gametophyte plant when in a suitable environment.
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Figure 14. This photograph shows the lobed leaf-like gametophyte plant at the bottom which is darker green in the center and lighter green towards the edges. It also shows the sporophytes projecting upward in their stalk structures having brown tips.
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