The forked ferns are the family Gleicheniaceae, which includes six genera and about 160 known species.[Smith et al. (2006)]
Description
These
tropical ferns are the most widespread living lineage of
Gleicheniales. Their
have a "vitalized"
protostele or in some
taxa a
solenostele. The leaves are indeterminate, with
dichotomy forked leaves except in
Stromatopteris, and free
leaf vein.
Stromatopteris also differs from the other species in having an achlorophyllous and subterranean
gametophyte.
[ Identifying cryptic fern gametophytes using DNA barcoding: A review] The
sorus are
abaxial but not marginal and carry 5–15
indusium round
sporangia each. These have a transverse-oblique annulus and contain 128 to 800 bilateral or globose-tetrahedral
. The sori and sporangia mature at the same time, and the spores grow into surface-dwelling green
prothallus beset with club-shaped hairs.
Systematics
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.
Phylogeny of Gleicheniaceae by Nitta et al. 2022
Footnotes
