Division: Pteridophyta (Filicophyta)
The leptosporangiate ferns are those with sporangia with similar annuli and with typically 64 spores per sporangium. These ferns plus the class Osmundopsida constitute the true ferns, with the Marattioids and Ophioglossoids actually being no more closely related to the true ferns than are seed plants.
The stem line of all pteridophytes and seed plants was apparently n=11. Within the leptosporangiate ferns, the first five orders, Gleicheniales through Marsileales, were apparently derived from polyploidy of n=11. Lindseales, Dennstaedtiales and Aspleniales were apparently derived from polyploidy of n=12, while Hypolepidales were probably derived from n=13. Pteridales may have developed from n=14, but this is much less clear. I propose that the subsequent orders, from Athyriales through Polypodiales, developed from a basal count of n=14 tripling through hexaploidy to n=42, then reducing to n=41, n=40, n=37, and so forth.
Orders of Pteridopsida:
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This page was last revised on 11-21-1997.