Gleicheniales is an order of ferns in the subclass Polypodiidae (the leptosporangiate ferns). The Gleicheniales has spore records potentially as early as the Early Carboniferous, but the oldest unambiguous macrofossil records date to the Early Permian.
Description
These ferns are characterized by root steles having 3–5 protoxylem poles and antheridia with 6–12 narrow, twisted or curved cells in their walls, The linear sequence of Christenhusz et al. (2011), intended for compatibility with the classification of Chase and Reveal (2009) which placed all land plants in Equisetopsida, reclassified Smith's Polypodiopsida as subclass Polypodiidae and placed the Gleicheniales there. The circumscription of the order and its families was not changed, and PPG I (2016).
The fossil taxon Microphyllopteris is used for some Mesozoic Gleicheniales that cannot be reliably assigned to the present-day orders. The Triassic Antarctipteris and Gleichenipteris are sometimes ascribed to the Gleicheniaceae, but are probably better considered Gleicheniales incertae sedis.<!-- see above - ref for Triassic fossils only -->
In historical treatments, the order has sometimes been treated as a subclass Gleicheniatae of the Pteridopsida, with the taxa treated as families here upranked to orders, so that a distinct subclass can be established for the leptosporangiate ferns. In other treatments, they were expanded to include the filmy ferns (order Hymenophyllales), as well as the similar-looking genus Hymenophyllopsis (as order Hymenophyllopsidales). The resultant group was treated as class Gleichenopsida alongside the Pteridopsida, which would then be limited to the leptosporangiate ferns. However, this class is not monophyletic but rather a basal grade, retaining ancient traits among the living ferns.
! colspan=1 |Nitta et al. 2022
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Footnotes
References
- (2006): A classification for extant ferns. Taxon 55(3): 705–731. PDF fulltext