Glossopteris - Biology

Biology

Glossopteris was a woody, seed-bearing shrub or tree, some apparently reaching 30 metres (98 ft) tall. They had a softwood interior that resembles conifers of the family Araucariaceae. Seeds were borne on one side of variably branched or fused structures, and microsporangia containing pollen were borne in clusters at the tips of slender filaments. Both the seed- and pollen-bearing organs were partially fused (adnate) to the leaves, or, in some cases, possibly positioned in the axils of 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). It is unclear whether glossopterids were monoecious or dioecious.

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 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 and were relatively widely spaced to take advantage of the low-angle sunlight at high latitudes. Instead of needles, they had large, broad lance- or tongue-shaped leaves that fell to the ground at the end of summer. The fossil leaves are commonly found as dense accumulations representing autumnal leaf banks. The broad fossilized growth rings in many Glossopteris woods reveal that the plants experienced strong growth spurts each spring-summer but underwent abrupt cessation of growth before each following winter.

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 have shown that taxa had more restricted regional distributions and several intra-gondwanan floristic provinces are recognizable. Seeds, much too large to be wind-borne, could not have blown across thousands of miles of open sea, nor is it likely they have 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.

The first Antarctic specimens of Glossopteris were discovered by members of Robert Scott's doomed Terra Nova Expedition. The expedition members abandoned much of their gear in an effort to reduce their load, but kept 35 pounds of Glossopteris fossils; these were found alongside their bodies.