Slide 1
A fern alternates between two plant forms
Ferns reproduce through spores rather than seeds. The leafy fern is one stage of a life cycle with two distinct plant forms.
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Ferns still have tissues that transport water and nutrients. Reproducing without flowers does not place them in the same structural group as small non-vascular mosses.
Slide 2
A spore grows into the reproductive-cell stage
A fern spore can grow into a small gametophyte. This stage produces reproductive cells rather than another crop of spores.
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The gametophyte may look very different from a fern frond. Its small size helps explain why people can know a fern well without ever noticing half of its life cycle.
Slide 3
Moisture lets sperm reach an egg
In the typical fern life cycle, sperm swim through moisture to reach an egg. Fertilization begins the next spore-producing generation.
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That need for water helps shape successful reproductive sites. A species can disperse spores into many places while producing new plants only where the smaller stage can survive and reproduce.
Slide 4
The new leafy fern grows on the smaller plant
The new leafy plant initially develops on the gametophyte. It later grows its own roots and leaves and becomes the familiar fern.
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Many ferns also spread through rhizomes, which are underground stems. This vegetative growth can enlarge a patch without repeating the entire sexual life cycle for each new frond.
Slide 5
Spore cases on its fronds restart the cycle
Clusters of spore cases often form on the underside of fertile fern fronds. Their arrangement can help distinguish different kinds of fern.
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Not every frond is fertile, and arrangements differ among species. Looking for reproductive structures provides another identification clue beyond the overall outline of a green leaf.
Sources
- Pteridium aquilinum, western brackenfern
US Forest Service
- Seedless Vascular Plants
OpenStax Rice University