''Gleichenia'' is a

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

fern The ferns (Polypodiopsida or Polypodiophyta) are a group of vascular plants (plants with xylem and phloem) that reproduce via spores and have neither seeds nor flowers. They differ from mosses by being vascular, i.e., having specialized tissue ...

s. Its closest relative is the genus '' Stromatopteris'', restricted to

New Caledonia New Caledonia ( ; ) is a group of islands in the southwest Pacific Ocean, southwest of Vanuatu and east of Australia. Located from Metropolitan France, it forms a Overseas France#Sui generis collectivity, ''sui generis'' collectivity of t ...

Description

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). The sori occur in a unique chamber in the laminar pits - a feature found only in this genus.

Fossil record

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 The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 77.1 million years, it is the ninth and longest geologi ...

. There is some evidence that it may have emerged even earlier - in the upper

Triassic period The Triassic ( ; sometimes symbolized 🝈) is a geologic period and system which spans 50.5 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.4 Mya. The Triassic is the ...

. 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. Fossils have been found in across a wide geographic range including: * The Pariwar formation in

India India, officially the Republic of India, is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area; the List of countries by population (United Nations), most populous country since ...

(Jurassic-Cretaceous boundary) * Gardeshwar in India (early Cretaceous) * The Silty Beds of

Bedfordshire Bedfordshire (; abbreviated ''Beds'') is a Ceremonial County, ceremonial county in the East of England. It is bordered by Northamptonshire to the north, Cambridgeshire to the north-east, Hertfordshire to the south and the south-east, and Buckin ...

England England is a Countries of the United Kingdom, country that is part of the United Kingdom. It is located on the island of Great Britain, of which it covers about 62%, and List of islands of England, more than 100 smaller adjacent islands. It ...

(early Albian age, early Cretaceous). * The USA (Cretaceous) * New South Wales, Australia (

Miocene epoch The Miocene ( ) is the first geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and means "less recent" ...

, Neogene period)

Phylogeny

The following species are recognised as of February 2023: Phylogeny of ''Gleichenia'' Unassigned species: * '' Gleichenia alstonii'' Holttum * '' Gleichenia elongata'' Baker * '' Gleichenia matthewii'' Holttum * '' Gleichenia paleacea'' (Copel.) Holttum * '' Gleichenia peltophora'' Copel. * '' Gleichenia ×punctulata'' Colenso * '' Gleichenia vulcanica'' Blume

References

External links

Smith's original description of the genus online at Project Gutenberg
Fern genera {{Polypodiidae-stub