Gleichenia

These ferns have creeping rhizomes. The compound eaves fork multiple times, with the final leaf lobes ending in a pinnate arrangement. The sori are found at the bottom of the leaves and are made of a few sporangia. They are not covered by an indusium (protective covering).^[4] The sori occur in a unique chamber in the laminar pits - a feature found only in this genus.^[5]

The fossil record indicates that this genus had emerged by the late Jurassic period, although it was far more common in the early Cretaceous period.^[6] There is some evidence that it may have emerged even earlier - in the upper Triassic period.^[7] There are, however, multiple genera in the fossil record that show a similar leaf branching pattern to Gleichenia, which can make it difficult to determine the exact identity of a specimen that does not have adequately preserved fruiting bodies.^[8]

Fossils have been found in across a wide geographic range including:

• The Pariwar formation in India (Jurassic-Cretaceous boundary)
• Gardeshwar in India (early Cretaceous)^[9]
• The Silty Beds of BedfordshireinEngland (early Albian age, early Cretaceous).^[10]
• The USA (Cretaceous)^[7]
• New South Wales, Australia (Miocene epoch, Neogene period)^[5]

The following species are recognised as of February 2023:^{[1][2][11][12]}

Phylogeny of Gleichenia^[13][14]

Unassigned species:

• Gleichenia alstonii Holttum
• Gleichenia elongata Baker
• Gleichenia matthewii Holttum
• Gleichenia paleacea (Copel.) Holttum
• Gleichenia peltophora Copel.
• Gleichenia ×punctulata Colenso
• Gleichenia vulcanica Blume

• Smith's original description of the genus online at Project Gutenberg