Variations of fern spore ultrastructure as reflections of their evolution

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Abstract
The spores of five species each of Bolbitis, Teclaria, Polybotria, Elaphoglossum, Ctenitis, Arthropteris, Lomariopsis, Davallia, Nephrolepis, Leucostegia, Oleandro and Humata, all genera of tropical ferns, were studied by light, scanning, and transmission electron microscope. Spore features were then compared and used to determine natural relationships. An exospore wall and a perispore wall were observed in spores of every species, including some that had previously been described as lacking a perispore. The exospore is stratified into two layers in the area of the aperture. The perispore may be unilayered, bilayered or multilayered. In some cases the perispore exhibits a columella‐like structure that resembles the exine of angiosperm pollen. This study indicates that spore characteristics can be used to show relationships among species and genera of ferns.