| Fern spore have either of two distinct shapes, monolete and trilete. Monolete spores are more or less bean-shaped(eg.
Drynaria, Humata and Histiopteris). Trilete spores
are more or less like triangle, meet together on three faces (eq. Dicranopteris, Osmanda, Lygodium,
Pteris and Cibotium). The exine wall of spore is resistance to environmental influences.
They are definitely conservative and correspond to groups of related species, genera, or even to whole families.
Hence fossil spores give objective information on the origin and history of the fern taxa.
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