Gleicheniaceae

The forked ferns are the family Gleicheniaceae, which includes six genera and 165 known species. They are sometimes – like all ferns – placed in an infradivision Monilophytes of subdivision Euphyllophytina, allowing for more precise phylogenetic arrangement of the tracheophytes. More conventionally, the name Pteridophyta, ranked as a division, is used in lieu of the Monilophytes. The formerly independent families Dicranopteridaceae and Stromatopteridaceae are nowadays generally included in the Gleicheniaceae, whereas the Dipteridaceae and Matoniaceae, though closely related, are considered spearate families by most authors. These tropical ferns are the most widespread living lineage of Gleicheniales. Their rhizomes have a 'vitalized' protostele or in some taxa a solenostele. The leaves are indeterminate, with pseudodichotomously forked leaves except in Stromatopteris, and free veins. The sori are abaxial but not marginal and carry 5–15 exindusiate round sporangia each. These have a transverse-oblique annulus and contain 128 to 800 bilateral or globose-tetrahedral spores. The sori and sporangia mature at the same time, and the spores grow into surface-dwelling green prothalliums beset with club-shaped hairs. There is some dispute about ranking these ferns. They are typically placed in the order Gleicheniales. They may alternatively be considered a subclass Gleicheniatae or class Gleichenopsida, so that a distinct taxon can be established for the leptosporangiate ferns. In this case, the Gleicheniaceae are upranked to an order and receive the name Gleicheniales. Irrespective of their modern taxonomic treatment, the Gleicheniaceae were formerly included in the order Polypodiales. But the ferns in the loose sense are much too diverse a group to be shoehorned into one taxon at such a low rank. The Triassic Antarctipteris and Gleichenipteris are sometimes ascribed to the Gleicheniaceae, but are probably better considered Gleicheniales incertae sedis. The six extant genera are: