Australia: The Land Where Time Began

A biography of the Australian continent 

Horsetails of the Giant Clubmoss Flora

In the Northern Hemisphere flora of swamps Calamites, or Giant Horsetails, were co-dominants. They are present in Australia, but as this continent didn't have the optimum conditions they experienced in the Northern Hemisphere swamps, the Australian varieties never achieved the size or luxuriance of their northern relatives.

In both the extinct and the extant horsetails, the stems are jointed. The whorls of leaves and branches are produced at each joint, and terminal cones are their reproductive structures. They also have an effective means of vegetative propagation, sending underground rhizomes that intermittently produce erect stems that grow upward and become the stems of new plants. The result is that they form dense thickets similar to those of bamboo.

As with some forms of giant clubmosses, some of the very large tree forms from the fossil deposits had produced what were in effect seeds, following the sequence of heterospory to retained female egg to seeds. The small horsetails that survived the loss of their preferred habitat continued to grow until the present on the edges of swamps and along rivers. At least part of the explanation of why they are so common in the fossil record is that they grew, and grow,  in locations where they are most likely to be fossilised.

Sources & Further reading

  1. Maey E. White, The Greening of Gondwana, the 400 Million Year story of Australian Plants, Reed, 1994


Author: M. H. Monroe
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