The Ferns have been classified by their fruit, which consists of minute one-celled powder-like spores in a case (sporangium). The sporangia are often clustered into round or oblong dots (sori), and these are sometimes covered by a thin skin (indusium).
1. Polypodium and Phegopteris, sori round and uncovered.
2. Petris and Adiantum, sporangia covered by the edge of leaf.
3. Woodwardia, sori oblong, parallel to ribs.
4. Asplenium, sori oblong, oblique to ribs, and opening inwards.
5. Dicksonia, indusium cup-shaped, supported by a tooth of the leaf.
6. Woodsia, indusium hood-like, covering the sporangia.
7. Cystoperis, indusium fastened behind sori, opening from the centre.
8. Aspidium, indusium kidney or shield shaped, fastened at the middle, opening all round.
9. Onoclea, fertile on separate contracted fronds, sporangia covered with deformed leaves.
10. Osmunda and Botrychium, sporangia uncovered, and separate.
11. Lygodium, indusium scale-like, covering the sporangia.
12. Ophioglossum, sporangia uncovered, and connected.
