This group includes all the true ferns, that is, the Marattioid ferns, Osmundoid ferns plus the leptosporangiate ferns. The Ophioglossoids are apparently no more closely related to the true ferns than are seed plants. The same argument could possibly be made for the Marattioids as well, but they are probably still phyletically consistent with their position in the Division Pteridophyta. It's probably true that the Marattioids diverged much more anciently than did the Osmundoids.
The stem line of all pteridophytes and seed plants was apparently n=11. Within the Pteridophyta, alterations in this basal number and polyploidy based on those alterations and n=11 was instrumental in developing a large variety of types of ferns. The median chromosome count for true fern species is probably between n=35 and n=40. However, as seen in genera such as Ophioglossum, Schizaea, Vittaria, and Elaphoglossum, very high polyploid chromosome counts often result in reduction of vegetative featur es.
Classes of Pteridophyta:
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This page was last revised on 11-10-1997.