Everything about Glossopteris totally explained
Glossopteris (
Greek glossa, meaning "tongue", because the leaves were tongue-shaped) is the largest and best-known
genus of the
extinct order of
seed ferns known as
Glossopteridales (or in some cases as Arberiales or Dictyopteridiales). Long considered a
fern after its discovery in 1824, it was later assigned to the
gymnosperms. The genus is placed in the division
Pteridospermatophyta. In reality, many of the plant groups included within this division are only distantly related to one another.
Glossopteris should strictly be used to refer to the distinctive spathulate fossil leaves with reticulate venation, however, the term has also been used to refer to the parent plant as a whole.
Glossopteris was a woody, seed-bearing shrub or tree, some apparently reaching 30 m tall. They had a softwood interior that resembles conifers of the family
Araucariaceae. Seeds and
pollen-containing organs were borne in clusters at the tips of slender stalks partially fused (adnate) to the leaves. The homologies of the flattened seed-bearing structures have remained particularly controversial with some arguing that the fertile organs represent megasporophylls (fertile leaves) whereas others have interpreted the structures as flattened, seed-bearing, axillary axes (cladodes).
They are interpreted to have grown in very wet
soil conditions, similar to the modern
Bald Cypress. The leaves ranged from about 2 cm to over 30 cm in length.
The Glossopteridales arose around the beginning of the
Permian on the great southern continent of
Gondwana. These plants went on to become the dominant elements of the southern flora through the rest of the Permian but disappeared in almost all places at the end of the Permian. The only convincing Triassic records are very earliest Triassic leaves from Nidpur in India, but even these records are somewhat questionable owing to faulting and complex juxtapositioning of Permian and Triassic strata at Nidpur. Although most modern palaeobotany textbooks cite the continuation of glossopterids into later parts of the Triassic and, in some cases into the Jurassic, these ranges are erroneous and are based on misidentification of morphologically similar leaves such as
Gontriglossa,
Sagenopteris, or
Mexiglossa. Glossopterids were, therefore, one of the major casualties of the Permian-Triassic mass-extinction event.
The profile of glossopterid trees is largely speculative as complete trees have not been preserved. However, based on analogies with modern high-latitude plants
Glossopteris trees probably tapered upwards like a
Christmas tree. Instead of needles, they'd large, broad lance- or tongue-shaped leaves that fell to the ground at the end of summer. The fossilized tree rings in the
Glossopteris trees reveal that they grew steadily each summer and abruptly stopped for winter.
More than 70
fossil species of this genus have been recognized in
India alone, with additional species from
South America,
Australia,
Africa, and
Antarctica. Apart from those in India, only a few fossils from the northern hemisphere have been assigned to this group, but these are not identified with great certainty. For example, specimens assigned to
Glossopteris from the far east of Russia in the 1960s are more likely to be misdentifications of other gymnosperms such as
Pursongia. Confident assignment of fossil leaves to
Glossopteris normally requires their co-preservation with the distinctive segmented roots of this group (called
Vertebraria) or with the distinctive fertile organs.
Glossopteris leaves are morphologically simple so there are few characters that can be used to differentiate species. Consequently, many past researchers have considered the Permian
Glossopteris flora to be rather homogeneous with the same species distributed throughout the
Southern Hemisphere. However, more recent studies of the more morphologically diverse fertile organs has shown that taxa had limited regional distributions and several intra-gondwanan floristic provinces are recognizable. Nevertheless, several species of leaves found in Antarctica are common in the rocks of similar geologic age in India, located north of the
equator and half a world away. Seeds, much too large to be windborne, couldn't have blown across thousands of miles of open sea, nor could they've floated across vast oceans. Observations such as these led the
Austrian geologist
Eduard Suess to deduce that there had once been a land bridge between these areas. He named this large land mass
Gondwanaland (named after the district in India where the plant
Glossopteris was found). These same observations would also lend support to Alfred Wegener's
Continental drift theory.
Further Information
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