''Dicroidium'' is an extinct genus of fork-leaved

seed fern A seed is an Plant embryogenesis, embryonic plant enclosed in a testa (botany), protective outer covering, along with a food reserve. The formation of the seed is a part of the process of reproduction in seed plants, the spermatophytes, includ ...

s that were widely distributed over Gondwana during the

Triassic The Triassic ( ) is a geologic period and system (stratigraphy), system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago (Year#Abbreviations yr and ya, Mya), to the beginning of the Jurassic Period 201.36 ...

(). Their fossils are known from

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, the Arabian Peninsula, Australia,

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, the

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and

Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean, it contains the geographic South Pole. Antarctica is the fifth-largest cont ...

. They were first discovered in Triassic sediments of Tasmania by Morris in 1845. Fossils from the Umm Irna Formation in

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and in

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indicate that these plants already existed in Late

Permian The Permian ( ) is a geologic period and System (stratigraphy), stratigraphic system which spans 47 million years from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.9 Mya. It is the last ...

. Late surviving members of the genus are known from the

Early Jurassic The Early Jurassic Epoch (geology), Epoch (in chronostratigraphy corresponding to the Lower Jurassic series (stratigraphy), Series) is the earliest of three epochs of the Jurassic Period. The Early Jurassic starts immediately after the Triassic-J ...

(

Sinemurian In the geologic timescale, the Sinemurian is an age and stage in the Early or Lower Jurassic Epoch or Series. It spans the time between 199.3 ± 2 Ma and 190.8 ± 1.5 Ma (million years ago). The Sinemurian is preceded by the Hettangian and ...

) of East Antarctica. Within paleobotany, ''Dicroidium'' is a form genus used to refers to the leaves, associated with ovuluate organs classified as '' Umkomasia'' and pollen organs classified as '' Pteruchus,'' while ''Dicroidum'' is also used collectively to refer to the whole plant. Dicroidium zuberi leaf

Description

The leaves are similar to those of modern

fern A fern (Polypodiopsida or Polypodiophyta ) is a member of a group of vascular plants (plants with xylem and phloem) that reproduce via spores and have neither seeds nor flowers. The polypodiophytes include all living pteridophytes exce ...

s but like all seed ferns (

Pteridospermatophyta The term Pteridospermatophyta (or "seed ferns" or "Pteridospermatopsida") is a polyphyletic group of extinct seed-bearing plants (spermatophytes). The earliest fossil evidence for plants of this type is the genus ''Elkinsia'' of the late Devonia ...

) were thick and had substantial cuticles. ''Dicroidium'' differs from other seed fern leaves in having a forked rachis; giving the appearance of two fern leaves joined at the base. These plants had male and female reproductive structures. Following the form generic nomenclature of paleobotany, male pollen-bearing structures are separately named '' Pteruchus'' and the female structures '' Umkomasia''.

Whole plant reconstructions

Different organs attributed to the same original plant can be reconstructed from co-occurrence at the same locality and from similarities in the stomatal apparatus and other anatomical peculiarities of fossilized cuticles. *'' Dicroidium odontopteroides'' may have been produced by the same plant as '' Umkomasia macleanii'' (ovulate structures) and '' Pteruchus africanus'' (pollen organs). *'' Dicroidium zuberi'' may have been produced by the same plant as '' Umkomasia feistmantelii'' (ovulate structures) and '' Pteruchus barrealensis'' (pollen organs)

References

* Bomfleur, B. and Kerp, H. (2010). ''Dicroidium diversity in the Upper Triassic of north Victoria Land, East Antarctica.'' Triassic plants Fossil taxa described in 1912 Pteridospermatophyta {{Triassic-plant-stub